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Using IP

This document describes the Internet Protocol (IP) implementation and includes the following sections:

Internet Protocol Overview

Configuring IP

Other Configuration Tasks

IP Commands

Internet Protocol Overview

IP is a network layer protocol that provides a connectionless service for the delivery of data. The fact that it is connectionless makes IP an unreliable protocol, one that tries but does nothing to guarantee the delivery of data. As used on the Internet, IP is the package used to carry data; actual delivery of the data is assured by transport layer protocols like TCP (Transmission Control Protocol).

The Nx Networks IP implementation conforms to standards defined by the TCP/IP protocol suite.

IP Addresses

IP addresses identify where a host's interface attaches to the IP network or a particular network segment. If, for example, a host has more than one interface attached to the network, that host would have an IP address for each connection. This makes an IP address much like a postal street address, indicating where to send the data, not to whom to send the data.

An IP address is a 32-bit number in the header of an IP datagram that encodes network segment identification, as well as identification of a unique host on that network. This 32-bit number is commonly represented in dotted decimal notation. In this notation, each decimal integer represents one octet of the 32-bit address.

Thus a 32-bit IP address, in base 2

10000000 00001010 0000010 00011110

is written as the following set of decimal numbers:

128.10.2.30

Each IP address forms a pair of identifiers, the netid and the hostid.

IP Address Classes

 IP addresses have three primary forms of designation: Class A, Class B, and Class C. A host determines the class of IP address by examining the high order bits of the address.

Figure 1 IP Address Classifications

This implementation of IP lets you assign multiple IP addresses on the same interface. Multiple IP address provide flexibility when

Notes:

Subnet Addresses

 The concept of subnet addressing or subnetting allows a site with multiple physical network segments to use a single IP network number. Subnetting adds another level of hierarchy to the internet addressing structure. Instead of a 2-level (netid, hostid) hierarchy, there is now a 3-level (netid, subnetid, hostid) hierarchy. An organization is then assigned one, or at the very most, a few IP network numbers. An organization is then free to assign a distinct subnet number to each of its physical network segments (LANs and WANs).

An organization's subnet structure is never visible outside the organization's network from a host (or router) located anywhere on the internet. It gives the organization the freedom to administer its internal network segments without having to deal with internet management.

Conceptually, adding subnetting only changes the interpretation of the IP address. Subnetting divides the address into a network ID, subnet ID, and host ID as shown in Figure 2. A combination of network ID and subnet ID identifies the network segment.

There is no set standard for the width of the subnet part; it can be a few bits wide to most of the width of the hostid field.

Figure 2 Subnet Concept

Subnet Mask

When adding an IP address to an interface, you must specify the subnet mask.

Subnet masks identify the portion of the address occupied by the netid and the subnetid. The mask is simply another 32-bit string written in dotted decimal notation with all ones in the network and subnet portion of the address.

For example, suppose you have a class B address. You want to assign the first 8 bits of the hostid as the subnet id. Following the rule of placing all ones in the netid and subnetid fields, you get a a mask of 255.255.255.0 as shown in Figure 3.

Figure 3 8-bit Subnet Mask

The subnetid can consist of any number of host field bits that do not have to be multiples of eight. For example, you may want to assign the first ten bits of the hostid as the subnetid. This creates a mask of 255.255.255.192. Figure 4 illustrates this mask.

Figure 4 10-bit Subnet Mask

You should use three or more bits for a subnet id; a subnet id of two bits yields only four subnets, two of which are reserved (the 1,1 and 0,0 values).

Table 1 shows the subnet masks subnet and host fields that you can get from dividing an octet.

Table 1 Subnet Masks
Subnet Bits Host Bits Byte of
Hex Mask 		Byte of
Decimal Mask
0

 8

 0

 0

1

 7

 0x80

128

2

 6

 0xC0

 192

3

 5

 0xE0

 224

4

 4

 0xF0

 240

5

 3

 0xF8

 248

6

 2

 0xFC

 252

7

 1

 0xFE

 254

Note: All interfaces running RIP must have the same subnet mask.

The Nx Networks IP implementation supports variable-length subnets. This feature lets you divide the hostid of a single IP network number into many variable size subnets. For example, 128.185 could have a subnet 128.185.22.0 with subnet mask of 255.255.255.0 (giving a size of 254 possible hosts) and a subnet 128.185.23.16 with mask 255.255.255.240 (giving a size of 14 possible hosts).

You can use variable-length subnets only with dynamic routing protocols that distribute each destination's subnet mask (that is, OSPF protocol). IP also allows static routing information to take advantage of variable-length subnetting.

CAUTION:
Assign variable length subnets with care. If you assign a subnet in an overlapping fashion, problems may occur.

If you are planning to connect your networks and routers to the Internet, talk to your Internet Service Provider, the Internic (http://rs.internic.net), or the address registry in your country to get IP addresses.

Autonomous Systems

The other main facet of IP addressing is the Autonomous Systems (AS). In a large internet, there is not a single administrative authority. Rather, the system consists of many cooperating groups. Often each group wants to retain a high degree of control over its piece of the system to prevent contamination from problems elsewhere in the system.

For this purpose, groups of routers are arranged into autonomous systems. AS's are numbered sequentially by 16-bit identifiers with no structure. There is no direct connection between IP addresses and AS numbers. The Internic (http://rs.internic.net) assigns AS numbers. Typically an organization is assigned a single AS number.

The following section on IP Routing further describes the function of autonomous systems.

IP Routing

IP uses routing tables to decide where to send a packet. The routing table is a list of all the network segments that IP knows how to reach. The routing table contains both dynamic and static routes.

A dynamic route is one that the router learns through a routing protocol, such as the Routing Information Protocol (RIP). RIP regularly updates the routing tables as network conditions change. Dynamic routing allows the router to transmit packets around network failures.

A static route is a route that never changes. You must enter a static route when configuring IP. Static routes persist across power-downs, restarts, and software reloads. The router uses them when for some reason it cannot determine the correct dynamic route.

IP routing happens as follows:

1. IP receives the packet and reads the 32-bit destination address it finds within the packet header.

2. If the packet is destined for this router, further routing is not necessary and IP hands the packet to the appropriate internal software module. Packets in this category include the following:

3. If the packet is destined for a host on a directly-connected network segment, IP matches the 32-bit destination address with the appropriate physical address in the Address Resolution Protocol (ARP) table. IP then hands the packet to the appropriate lower-level protocol module for transmission directly to the destination node.

4. If the packet is destined for a host on a remote network segment, IP uses the routing table to determine which router leads to that network segment. Each entry in the routing table contains a destination address and the IP address of the next hop router. If IP matches the destination address in the table with the destination contained in the packet, it hands the packet to the appropriate lower-level protocol for transmission to that next hop.

5. If the packet has no entry for its IP address in the routing table, IP routes the packet to the default router. Default routers route packets whose destination address is not found in the routing table. This router is assumed to know the location of the packet's destination. See Default Routers (Gateways).

IP also performs several other major tasks:

Default Routers (Gateways)

 A default gateway knows how to route packets that other routers cannot route. There are two kinds of default gateways:

You can specify a router (static route) where IP should route packets that it cannot route using its own routing table; or, the router can learn about the default gateway by using the RIP or Open Shortest Path First (OSPF) protocols. Both protocols represent the default route as destination 0.0.0.0.

Note: Not all router loads include OSPF.

In Figure 5, the network segments are 13.101.0.0, 13.102.0.0, 13.103.0.0, 13.104.0.0, and 9.105.0.0. The routers are Azure, Blue, Cobalt, and Dresden; where Dresden is the default network gateway because it has knowledge of network 13 and any other networks. Network 13 routers do not have any knowledge of networks outside network 13.

On network segment 13.104, unknown-network traffic goes first to router Dresden then toward the appropriate destination.

Figure 5 Internet with Default Gateway (Dresden)

Martian Filtering

Martian is a humorous term that applies to packets that are incorrectly formatted or have an improper destination address. The router drops these packets to ensure that Martians are not forwarded further into the network.

Address filtering ensures that IP does not forward any packets to those specified addresses, nor does it broadcast any routing information it receives concerning those addresses. For example, address 127.0.0.0 is used as a local loop-back address in BSD-derived UNIX-based operating systems. You should install filters on your routers to ensure that your routers receive and relay only packets with valid IP addresses.

Unnumbered Serial Lines

This implementation of IP allows you to send IP traffic over a serial line interface without assigning an IP network number to that line. This feature allows you to configure static routes across the line to the next hop router or to a default gateway; however, this feature also includes the following restrictions on certain diagnostic capabilities:

Dynamic IP Address Assignment

You can set up unnumbered PPP serial line interfaces so that the remote router or server dynamically assigns an IP address to the interface. See Assigning IP Addresses to Interfaces.

Router ID

The router ID is the default IP address that IP uses when sourcing various kinds of IP traffic. When you set the router ID, the router ID becomes the source IP address in all locally-originated IP packets either that the router sends over unnumbered serial lines or that are multicasts.

Internal IP Address

The internal IP address is an address that belongs to the router as a whole, and not any particular interface. The router uses it only when the router needs to be assured of always having a particular address available or when the router is the source of many multicast packets, for example, when the router is running IP multicast bridging tunnel.

When you set the internal IP address,

Note: You should use the internal IP address only when there is a definite need to have an IP address that is always reachable, regardless of what interfaces are operational.

Receiving IP Broadcasts

 IP recognizes all forms of broadcast messages and addressing. If the network portion of the broadcast address indicates either local wire or a directly-connected IP network, IP treats the packet as if it is addressed to itself.

IP also forwards directed broadcasts. A directed broadcast is a broadcast destined for networks other than the networks on which it originated. By enabling IP's directed-broadcast feature, you can forward IP packets whose destination is a nonlocal (for example, remote LAN) broadcast address. For example, the source host originates a unicast packet. IP then forwards the packet, as a unicast, to a destination subnet and explodes the packet into a broadcast. You can use this feature to locate network servers and to enable both the forwarding and exploding of directed broadcasts. The default setting for the directed broadcast is enabled.

IP Multicast Routing

The IP protocol also supports IP multicast routing through IP multicast extensions to OSPF (MOSPF). (This is only true if your router software supports OSPF.)

The following existing TCP/IP applications take advantage of the multicast support this MOSPF implementation provides:

Tunneling Other Network Protocols Over IP

 To allow IBM LAN and terminal traffic to merge with non-IBM traffic (for example, Digital and Novell) across a single backbone, the Source Routing Bridge Tunnel and SDLC (Synchronous Data Link Control) Relay features of the router software encapsulate IBM traffic within industry-standard TCP/IP packets. The router then routes these packets using an IP path or tunnel through large IP internetworks. The benefit is increased functionality and network utilization, as well as higher network availability and increased ease of use.

End stations see the IP path (the tunnel) as a single hop, regardless of the network complexity. This helps overcome the usual seven-hop distance limit encountered in source routing configurations. It also lets you connect source routing end stations across nonsource routing media, such as Ethernet networks.

The bridging tunnel also overcomes several limitations of regular source routing, including the following:

With the bridge tunnel feature enabled, the software encapsulates packets in TCP/IP packets. To the router, the packet looks like a TCP/IP packet. Once the software encapsulates a frame in an IP envelope, the IP forwarder is responsible for selecting the appropriate network interface based on the destination IP address. The IP forwarder can router this packet dynamically through large internetworks without degradation or network size restrictions. End stations see this path or tunnel, as a single hop, regardless of the complexity of the internetwork.

The tunnel is transparent to the end stations. The routers participating in tunneling treat the IP internet as one of the bridge segments. When the packet reaches the destination interface, the software automatically removes the TCP/IP headers and the inner packet proceeds as a standard source routing packet.

Encapsulation and OSPF

A major benefit of the encapsulation feature is the addition of the OSPF dynamic routing protocol to the routing process. OSPF offers the following benefits when used with encapsulation:

With OSPF, tunnels automatically manage paths inside the internetwork. If a line or bridge fails along the path then the tunnel bridge automatically reroutes traffic along a new path. If a path is restored, the tunnel automatically updates to the best path. This rerouting is completely transparent to the end stations.

Configuring IP

This section outlines the initial steps required to configure IP. After completing these tasks, restart the router for the new configuration to take effect. The following sections discuss each configuration task in more detail.

1. Display the IP configuration prompt.

2. Assign IP addresses to network interfaces.

3. Add static routing information (optional).

4. Enable ARP subnet routing.

5. Exit the IP configuration process.

6. Restart the router to activate the configuration changes.

Displaying the IP Configuration Prompt

 To access the IP configuration environment, enter the following command at the Config> prompt:

Config>protocol IP
IP config>

Assigning IP Addresses to Interfaces

 IP automatically becomes enabled whenever you assign at least one IP address to any of the router's interfaces. An interface does not accept or send IP packets unless it has at least one IP address.

Use the add address command to assign IP addresses to the network interfaces. You can obtain the net (interface) number using the list interface command at the Config> prompt.

IP allows you to use a serial line interface for IP traffic without assigning an IP address to the line. However, you must still assign each serial line a label. Use the add address command to assign the serial line an address of the form 0.0.0.n, where n is the interface number (again obtained from the list interfaces command). This address format tells the router that the interface is an unnumbered serial line.

For PPP interfaces, you can set up unnumbered serial lines so that the router or server at the other end of the PPP link dynamically assigns an IP address for the interface. The router uses PPP's IP Control Protocol (IPCP) address negotiation. To set up a PPP interface for dynamic address assignment, follow these steps:

1. At the IP Config> prompt enter add address.

2. Enter an unnumbered serial line address (0.0.0.n) for the PPP interface.

3. Respond Yes to the prompt that asks if you want to allow dynamic address assignment.

4. You must enter an address mask because IPCP cannot exchange network masks. Use the mask default of 255.255.255.0. 

IP config>add address
Which net is this address for [0]? 1
New address [0.0.0.0]? 0.0.0.1
Allow dynamic address assignment(Yes or [No]): yes
Address mask [255.255.255.0]?

Adding Static Routing Information

 This procedure is necessary only if you cannot gain routing information from RIP or OSPF. Static routing persists over power failures and the router uses it for routes that never change or for routes the router cannot learn dynamically. Static routing information consists of any of the following items:

Default Network Gateway

 Routers send packets having unknown destinations (destinations not present in the routing table) toward the default gateway. Configure a default gateway by specifying the next hop to use to get to the default gateway and the cost of sending packets to the default gateway.

In the following example, the next hop toward the default gateway is 192.9.1.4 and the cost of sending a packet to the default gateway is 5.

IP Config>set default network-gateway
Default gateway [0.0.0.0]? 192.9.1.4 
gateway's cost [0]? 5
Both OSPF and RIP can learn and advertise default gateways. For OSPF, you can configure a router to advertise itself as the default gateway with the following OSPF command:

OSPF Config>enable AS-boundary-routing
You can set up RIP to advertise the default gateway (if it has any) to its neighbors. You can also set up RIP so that a learned default gateway does (or does not) override a statically configured default gateway. You accomplish these tasks with the following RIP commands: 

RIP Config>enable/disable sending default-routes
RIP Config>enable/disable override default
If your network is attached to the Internet, then the boundary router, which connects your network to your Internet Service Provider (ISP), should have a default route pointing to your ISP. Since your router does not know of every route on the Internet, your router assumes any addresses it does not recognize are on the Internet and sends those packets to your ISP. Your IGP should then distribute the knowledge that the boundary router knows the default route (in this case, to the Internet) so that other routers know to send packets to unknown destinations to that router.

Default Subnet Gateway

You can configure a default subnet gateway for each subnetted network that the router knows about. When the router attempts to forward a packet to a destination belonging to the subnetted network, but it cannot find that destination in the routing table, it forwards the packet to the default subnet gateway.

Configuring a default subnet gateway is the same as configuring a Default Network Gateway. The only difference is that you must specify the subnetted network. For example, to create a default subnet gateway for the subnetted network 18.0.0.0, use the following command:

IP Config>set default subnet-gateway
For which subnetted network [0.0.0.0]? 18.0.0.0
Default gateway [0.0.0.0]? 128.185.123.22
gateway's cost [0]? 2
The above example specifies that the next hop to the subnet default gateway is 128.185.123.22, and that the cost of routing a packet to the default subnet gateway is 2.

Static Network/Subnet Route

You can set up static routes if you want a fixed route to a destination or if dynamic routing protocols cannot discover a destination. When dynamic routing information is not available for a destination, the router uses static routes.

Specify the route to the destination by the IP address of the next hop (Via gateway), and the cost of routing the packet to the destination. The next hop must be on the same (sub)net as one of the router's interfaces.

To create a static route, use the add route command.

IP Config>add route
IP destination [0.0.0.0]? 128.1.2.0
Address mask [0.0.0.0]? 255.255.255.0
Via gateway at [0.0.0.0]? 128.185.123.22
Cost [1]? 6
You can set up multiple routes to a destination. See add route for more information.

Use change route to modify a route and delete route to delete a route.

Routes dynamically learned through the OSPF and RIP protocols can override static routes. For RIP, you can disable this override behavior. See Setting RIP Flags.

Enabling ARP Subnet Routing

If there are hosts on attached subnetted networks that do not support IP subnetting, use Address Resolution Protocol (ARP) subnetting routing (described in RFC 1027). When you configure the router for ARP subnet routing, it replies by proxy to ARP requests for destination (that is, off the LAN if the router is itself the best route to the destination). For proper operation, configure all routers attached to a LAN containing subnetting-ignorant hosts for ARP subnet routing.

To enable ARP subnet routing, use the following command: 

IP Config>enable ARP-subnet-routing
Some IP hosts ARP for all destinations, whether or not they are attached to the local network segment. For these hosts, ARP subnet routing is not enough and you must see the proxy ARP functionality specified in RFC 925 instead. RFC 925 ARP routing is a subset of ARP subnet routing.

To enable RFC 925 ARP routing, use the following command: 

IP Config>enable RFC-925

Other Configuration Tasks

Configuring the BOOTP Forwarding Process

BOOTP (documented in RFC 951) is a bootstrap protocol diskless workstations use to learn their IP address and the location of their boot file and boot server. BOOTP requests/replies are forwarded at the application level (UDP). They are not forwarded at the network level. This means that the IP header changes as the packet is forwarded. The workstation broadcasts the request in a UDP packet to the routers, and in turn, the routers forward the packets to BOOTP servers.

The following terms are useful when discussing the BOOTP forwarding process:

The following steps outline an example of the BOOTP forwarding process:

1. The BOOTP client copies its Ethernet address (or appropriate MAC address) into a BOOTP packet and broadcasts it onto the local LAN. BOOTP is running on top of UDP.

2. The local BOOTP relay agent receives the packet and checks to see if the packet is well formatted and that the maximum number of application hops has not expired. It also checks to see if the client has tried long enough.

Note: If multiple hops are required before reaching the BOOTP agent, the packet is routed normally via IP. All other routers would not examine the packet to determine whether it is a BOOTP packet.

3. The Local BOOTP agent forwards a separate BOOTP request to each of its configured BOOTP servers. The BOOTP request is the same as the one that was initially sent by the client except that it has a new IP header with the relay agent's IP address copied into the body of the BOOTP request.

4. The BOOTP server receives the request and looks up the client's Ethernet address in its database. If found, it formats a BOOTP reply containing the client's IP address and boot file name. The reply is then sent to the BOOTP relay agent.

5. The BOOTP relay agent receives the reply and makes an entry in its ARP table for the client and then forwards the reply to the station.

6. The station then continues to boot using TFTP, using the information in the BOOTP reply packet.

To enable or disable BOOTP forwarding on the router, enter the following command at the IP configuration prompt. 

IP Config>enable/disable bootp
When enabling BOOTP, you are prompted for the following values:

After accepting a BOOTP request, the router forwards the BOOTP request to each BOOTP server. If there are multiple servers configured for BOOTP, the transmitting server replicates the packet.

To add a BOOTP server to the router's configuration, enter the following command at the IP configuration prompt:

IP Config>add BOOTP-SERVER IP-address-of-server
You can configure multiple servers. In addition, if only the network number of the server is known or if multiple servers reside on the same network segment, a broadcast address can be configured for the server.

Configuring UDP Broadcast Forwarding

The UDP (User Datagram Protocol) broadcast feature allows the router to forward UDP broadcast frames to specific IP addresses.

For example, NetBIOS uses UDP broadcasts in some client-server applications to broadcast Name-Query frames. Unless you set up UDP broadcast forwarding, the router drops those frames.

You can configure UDP broadcast so that the router directs frames to a network-level or subnet broadcast IP address. You can set up UDP broadcast to forward packets to the next destination by broadcasting to the next router, or to forward to the final destination by supplying a host address or directed broadcast address on the final network.

Follow these steps to configure UDP broadcast forwarding:

1. Add a UDP destination port number and IP address. The router maps this IP address to the UDP port. 

IP config>add udp-destination
UDP port number [-1]? 36
Destination IP address [0.0.0.0]? 20.1.2.2
2. Enable UDP forwarding. 

IP Config>enable udp-forwarding
For which UDP port number [-1]? 36
In this example, the router forwards frames it receives for UDP port 36 to IP address 20.1.2.1.

Enter list udp-forwarding to see the UDP broadcast configuration.

Configuring DHCP Server

To configure DHCP server, do the following:

1. Display the DHCP server configuration prompt.

2. Enable the DHCP server.

3. Set DNS, if you want your DHCP server to supply the DNS location to DHCP clients.

4. Set domain name.

5. Restart the router to activate the configuration changes.

Notes:

Configuring DHCP Client

 To configure a DHCP client on your router, do the following:

1. Add an IP address to your router's LAN interface that a DHCP server dynamically configures.

2. Restart the router to activate the configuration changes.

IP Commands

This section describes the IP configuration and monitoring commands.

Press Space twice after you type a command to display the available options for each command. Enter help for information about using the command line interface.

[C] means the command is available at the IP config> prompt.

[M] means the command is available at the IP> prompt.

Table 2 IP Commands

Command Function
Add [C] Adds interface addresses, bootp server, hostname, routes, and UDP broadcast destinations.

Cache [M] Displays a table of all recent routed destinations.

Change [C] Modifies information that you originally entered with the add command.

Counters [C] Lists various IP statistics, including counts of routing errors and packets dropped.

Delete [C] Deletes IP configuration information that you entered with the add command.

DHC [M] Displays the DHCP client prompt.

DHS [C] [M] Displays the DHCP server prompt.

Disable [C] Disables certain IP features that you turned on by the enable command.

Dump Routing Tables [M] Lists the contents of the IP routing table.

Enable [C] Enables IP features, such as ARP subnet routing, originate default, directed broadcasts, BOOTP, and UDP broadcasts.

Exit [C] [M] Exits the IP configuration or monitoring process.

Filters [C] [M] Displays the IP filtering prompts.

Hostnames [M] Displays the hostnames and IP addresses that you added using the add hostname command.

Interface Addresses [M] Lists the router's IP interface addresses.

List [C] Displays IP configuration items.

NAT [C] [M] Displays the Network Address Translation (NAT) prompts.

Ping [M] Sends ICMP echo requests to another host once a second and watches for a response. Use this command to isolate trouble in an internetworking environment.

RIP [C] [M] Displays the RIP prompts.

Route [M] Lists whether a route exists for a specific IP destination, and if so, the routing table entry that corresponds to the route.

Set [C] Sets IP parameters such as default routers and the size of the IP routing table.

Sizes [M] Displays the size of specific IP parameters.

Static Routes [M] Displays the static routes that have been configured including the default gateway.

Traceroute [M] Displays the complete path (hop-by-hop) to a particular destination.

UDP-Forward [M] Displays the UDP port numbers and destination IP addresses that you added using add udp-destination.

Add [C]

Adds IP addresses, BOOTP server, hostname, routes, and UDP destination.

Syntax: add

address
bootp-server
hostname
route
udp-destination

address interface-number IP-address address-mask

 Assigns an IP address to one of the router's interfaces. An interface does not receive or transmit IP packets until it has at least one IP address.

You must specify an IP address together with its subnet mask. For example, if the address is on a class B network, using the third byte for subnetting, the mask is 255.255.255.0. Use the list interface command to obtain the appropriate net number.

Serial lines do not need addresses. Such lines are called unnumbered. However, you must still enable them for IP traffic using the add address command. Use the address 0.0.0.n, where n is the net number. For PPP interfaces, you can set up unnumbered serial lines so that the router or server at the other end of the PPP link dynamically assigns an IP address for the interface. See Assigning IP Addresses to Interfaces.

Example: add address 

Which net is this address for [0]? 1
New address [0.0.0.0]? 0.0.0.1
Allow dynamic address assignment(Yes or [No]): yes
Address mask [255.255.255.0]?
You can add an address for a DHCP client.

Example: add address

Which net is this address for [0]?
New address [0.0.0.0]?
Allow dynamic address assignment via DHCP(Yes or [No]):yes
The software prompts you for whether or not to allow dynamic address assignment only if you enter an unnumbered serial line address (0.0.0.n).

bootp-server server-IP-address

Adds a BOOTP server to a network configuration. Acting as a boot relay agent, your router accepts and forwards BOOTP requests to the BOOTP server. BOOTP is a bootstrap protocol used by a diskless workstation to learn its IP address and the location of its boot file and boot server.

Example: add bootp-server

BOOTP server address [0.0.0.0]? 128.185.123.22

hostname

Provides hostname-to-IP address mapping. Enter an ASCII name and then the IP address to associate with the name. This command provides a function similar to the UNIX /etc/hosts file and the Microsoft Windows 95 LMhost file.

Example: add hostname

Hostname? 

IP address? 128.185.227.221

route IP-network/subnet/host IP-mask next-hop cost

 Adds a static network/subnet route. When dynamic routing information is not available for a destination, the router uses static routes.

You can also set up static routes to cause the router to always send traffic addressed to a destination over a specific interface, such as over an IP Tunnel interface.

You can add multiple static routes for a destination. In this case, the router determines which route to use based on the cost of the route.

Setting the address mask to 255.255.255.255 causes the router to discard traffic addressed to the IP destination. This is useful in situations where, if an interface goes down, you want the router to discard traffic rather than send the traffic over a different interface. For example, if an IP Tunnel goes down, you may want the router to discard traffic that was going through the tunnel rather than send the traffic over an interface that isn't set up to encrypt data. The router does not discard traffic if alternate routes of equal or lower cost to the destination are available.

Example: add route 

IP destination [0.0.0.0]? 128.1.2.0
Address mask [0.0.0.0]? 255.255.255.0
Via gateway at [0.0.0.0]? 128.185.123.22
Cost [1]? 6
IP destination

 IP address of the destination host, network, or subnet for which you want to add a static route.

Address mask

 IP address mask of the destination. Setting the mask to 255.255.255.255 causes the router to discard traffic to the destination. The router never discards traffic if alternate routes to the destination are available.

Via gateway at

 The next hop, which must be on the same (sub)net as one of the router's directly connected interfaces. You can enter the address of one of the router's interfaces, such as a PPP or Frame Relay interface or an IP Tunnel interface.

Cost

 The cost of routing the packet to the destination. If you set up multiple static routes to a destination, the router determines which route to use based on cost. The router sends traffic to the lowest cost route first. If that route goes down, the router sends traffic to the route that has the next lowest cost.

udp-destination port# address

Adds a UDP destination port number and IP address. See Configuring UDP Broadcast Forwarding for more information on this feature.

You can enter a broadcast, unicast, or multicast IP address.

Repeat this command to add more than one IP address for the same UDP port. This causes the router to forward the frame to each of the IP addresses.

Example: add udp-destination

UDP port number [-1]? 36
Destination IP address [0.0.0.0]? 20.1.2.2

Cache [M]

Displays the IP routing cache that contains recently routed destinations. If a destination is not in the cache, the router looks up the destination in the routing information table in order to make a forwarding decision.

Syntax: cache

Example: cache

Destination         Usage     Next hop

128.185.128.225     1         128.185.138.180       (Eth/0)
192.26.100.42       1         128.185.138.180       (Eth/0)
128.185.121.1       18        128.185.123.18        (PPP/0)
128.185.129.219     76        128.185.125.25        (PPP/1)
128.185.129.41      130       128.185.125.25        (PPP/1)
128.185.129.134     546       128.185.125.40        (PPP/1)
128.185.129.221     1895      128.185.125.40        (PPP/1)
128.185.129.193     96        128.185.125.40        (PPP/1)
128.197.3.4         4         128.185.123.18        (PPP/0)
128.185.128.25      98        128.185.125.41        (PPP/1)
128.185.124.121     4         128.185.124.121       (Eth/0)
128.185.136.203     95        128.185.125.39        (PPP/1)
128.185.194.4       581       128.185.125.39        (PPP/1)
128.185.123.17      2         128.185.123.17        (PPP/0)
192.26.100.42       1         128.185.125.38        (PPP/1)
128.52.22.6         2         128.185.123.18        (PPP/0)
128.197.3.2         1         128.185.123.18        (PPP/0)
128.185.126.24      61        128.185.125.25        (PPP/1)
128.185.138.150     482       128.185.125.39        (PPP/1)
128.185.123.18      152       128.185.123.18        (PPP/0)
Destination

IP destination host.

Usage

Number of packets recently sent to the destination host.

Next hop

IP address of the next router on the path toward the destination host. Also displays the network name of the interface the sending router used to forward the packet.

Change [C]

Changes an IP configuration item previously installed by the add command. In general, you must specify the item you want to change, just as you specified the item with the add command.

Syntax: change

address
route

address old-address new-address new-mask

 Modifies one of the router's IP interface addresses. You can also use this command to change an existing address' subnet mask.

Example: change address 

Enter the address to be changed [0.0.0.0]? 128.185.123.22
New address [128.185.123.22]? 128.185.123.8
Address mask [255.255.0.0]?
If you enter an unnumbered serial line address, the software prompts you for whether or not to allow dynamic address assignment.

Example: change address

Enter the address to be changed [0.0.0.0]? 128.185.123.22
New address [0.0.0.2]? 0.0.0.2
Allow dynamic address assignment? [Yes]:
Address mask [255.255.255.0]?

route destination old-mask new-mask 1st-hop cost

 Modifies either the subnet mask, next hop, or the cost associated with a configured static network/subnet route.

Example: change route 

IP destination [0.0.0.0]? 10.0.0.0
Address mask [0.0.0.0]? 255.0.0.0
New address mask [255.0.0.0]? 255.255.0.0
Via gateway at [0.0.0.0]? 128.185.123.18
Cost [1]? 6

Counters [C]

Displays the statistics related to the IP forwarding process. This includes a count of routing errors, along with the number of packets the router dropped due to congestion.

Syntax: counters

Example: counters

Routing errors
Count   Type
    0   Routing table overflow
 2539   Net unreachable
    0   Bad subnet number
    0   Bad net number
    0   Unhandled broadcast
58186   Unhandled multicast
    0   Unhandled directed broadcast
 4048   Attempted forward of LL broadcast

Packets discarded through filter  0
IP multicasts accepted:           60592

IP input packet overflows
   Net    Count
   Eth/0  0
   PPP/0  0 
   Eth/1  0
Routing table overflow

Routes discarded due to the routing table being full.

Net unreachable

Packets the router could not forward due to unknown destinations. This does not include the number of packets forwarded to the default gateway.

Bad subnet number

Packets or routes received for illegal subnets (all ones or all zeroes).

Bad net number

Packets or routes received for illegal IP destinations, such as class E addresses.

Unhandled broadcasts

Non-local IP broadcasts received (these are not forwarded).

Unhandled multicasts

IP multicasts received, but whose address was not recognized by the router (these are discarded).

Unhandled directed broadcasts

Directed (non-local) IP broadcasts received when forwarding of these packets is disabled.

Attempted forward of LL broadcast

Packets received having non-local IP addresses but were sent to a link level broadcast address. These are discarded.

Packets discarded through filter

 Packets received that were addressed to filtered networks/subnets. These are discarded silently.

IP multicasts accepted

 IP multicasts received and successfully processed by the router.

IP packet overflows

Packets discarded due to congestion at the forwarder's input queue. These counts are sorted by the receiving interface.

Delete [C]

Deletes an IP configuration parameter that you added with the add command. In general, you must specify the item you want to delete, just as you specified the item with the add command.

Syntax: delete

address
bootp-server
default network/subnet-gateway
hostname
route
udp-destination

address ip-interface-address

 Deletes one of the router's IP interface addresses.

Example: delete address 128.185.123.22

bootp-server server-IP-address

Removes a BOOTP server from an IP configuration.

Example: delete bootp-server 128.185.123.22

default subnet-gateway [subnetted network]

Deletes either the default gateway or the default subnet gateway for the specified subnetted network.

Example: delete default subnet-gateway 128.185.0.0

hostname hostname

Deletes a hostname that you entered using the add hostname command.

Example: delete hostname

Hostname?

route destination

 Deletes one of the router's configured static routes.

Example: delete route 10.0.0.0

udp-destination port# address

Deletes a UDP broadcast destination port that you configured using the add udp-broadcast command. See Configuring UDP Broadcast Forwarding for more information on this feature.

Example: delete udp-destination

UDP port number [-1]? 36
Destination IP address [0.0.0.0]? 20.1.2.2

DHC [M]

 From the IP> prompt, displays the DHCP Client> prompt.

DHS [C] [M]

From the IP config> prompt, displays the DHCP Server Config> prompt.

From the IP> prompt, displays the DHCP Server> prompt.

Disable [C]

Disables IP features previously enabled by the add command.

Syntax: disable

arp-subnet-routing
bootp-forwarding
directed-broadcast
ip-source-routing
per-packet-multipath
rfc925-routing
udp-forwarding

arp-subnet-routing

 Turns off the IP feature called ARP subnet routing or proxy ARP, which, when enabled, deals with hosts that have no IP subnetting support. This is the default and the generally recommended setting.

Example: disable arp subnet routing

bootp-forwarding

Turns off the BOOTP relay function.

Example: disable bootp-forwarding

directed-broadcast

Disables the forwarding of IP packets whose destination is a non-local (remote LAN) broadcast address. The source host originates the packet as a unicast where it is then forwarded as a unicast to a destination subnet and "exploded" into a broadcast. You can use these packets to locate network servers.

Note: Forwarding and exploding cannot be disabled separately.

Example: disable directed-broadcast

ip-source-routing

When IP source routing is disabled, IP does not include forwarding instructions for IP packet in the packet itself. IP source routing is disabled by default. Enabling IP source routing can pose a security risk because an attacker could learn information about your network.

Example: disable ip-source-routing

per-packet-multipath

Causes the router to choose the first available path to a destination. The default is disabled.

Example: disable per-packet-multipath

rfc925-routing

Turns off RFC 925 routing. When this enabled, the router replies by proxy to all ARP requests for remote destinations that are best reached through the router.

Example: disable rfc925-routing

udp-forwarding port#

Disables UDP broadcast forwarding that you previously enabled. See Configuring UDP Broadcast Forwarding.

Example: disable udp-forwarding

IP config>disable udp-forwarding
For which UDP port number [-1]? 36

Dump Routing Tables [M]

Displays the IP routing table. Lists a separate entry for each reachable IP network/subnet. The IP default gateway in use (if any) appears at the end of the display.

Syntax: dump routing tables

Example: dump routing tables

Type   Dest net         Mask       Cost     Age   Next hop(s)
RIP   9.0.0.0          FF000000   5        0     128.185.227.15
RIP   10.0.0.0         FF000000   3        0     128.185.227.15
RIP   50.0.0.0         FF000000   2        0     128.185.227.15
Sbnt  128.185.0.0      FFFF0000   1        0     None
RIP   128.185.1.0      FFFFFF00   4        0     128.185.227.15
RIP   128.185.2.0      FFFFFF00   4        0     128.185.227.15
RIP   128.185.224.0    FFFFFF00   2        30    128.185.227.15
RIP   128.185.225.0    FFFFFF00   2        30    128.185.227.15
Dir*  128.185.227.0    FFFFFF00   1        0     Eth/0
RIP   128.185.245.0    FFFFFF00   6        0     128.185.227.15
RIP   143.116.0.0      FFFF0000   5        0     128.185.227.15
RIP   162.6.0.0        FFFF0000   9        30    128.185.227.16
Dir*  162.9.0.0        FFFF0000   1        0     PPP/0
RIP   192.26.102.0     FFFFFF00   6        0     128.185.227.15
RIP   192.77.229.0     FFFFFF00   5        0     128.185.227.15
RIP   192.96.3.0       FFFFFF00   2        0     128.185.227.15
RIP   192.190.7.0      FFFFFF00   4        0     128.185.227.15
RIP   192.233.33.0     FFFFFF00   3        10    128.185.227.15
RIP   204.6.103.0      FFFFFF00   4        30    128.185.227.15
RIP   204.69.207.0     FFFFFF00   4        0     128.185.227.15
Routing table size: 768 nets (49152 bytes), 67 nets known
Type (route type)

Indicates how the route was derived.
Sbnt— the network is subnetted; such an entry is a placeholder only.
Dir— a directly connected network or subnet.
RIP— routes learned through RIP.
Del— the route was deleted.
Stat— the route is statically configured.
BGP— routes learned through BGP.
BGPR— routes learned through BGP that are readvertised by OSPF and RIP.
Fltr— a routing filter.
SPF— the route is an OSPF intra-area route.
SPIA— an OSPF inter-area routes.
SPE1, SPE2— OSPF external routes (type 1 and 2 respectively).
Rnge— a route type that is an active OSPF area address range and is not used in forwarding packets.
Dest net

 IP destination network/subnet.

Mask

 IP address mask.

Cost

 Route Cost.

Age

 For RIP routes, the time that has elapsed since the routing table entry was last refreshed.

Next Hop

 IP address of the next router on the path toward the destination host. Also displays the interface that the sending router used to forward the packet.

An asterisk (*) after the route type indicates that the route has a static or directly connected backup. A percent sign (%) after the route type indicates that RIP updates are always accepted for this network/subnet.

A number in parentheses at the end of the column indicates the number of equal-cost routes to the destination. Display the first hops belonging to these routes with the IP route command.

Enable [C]

Activates IP features, capabilities, and information added to your IP configuration.

Syntax: enable

arp-subnet-routing
bootp-forwarding
directed-broadcast
ip-source-routing
per-packet-multipath
rfc925-routing
udp-forwarding

arp-subnet-routing

 Turns on the router's ARP subnet routing (sometimes also called Proxy ARP) functionality. Use this functionality when there are subnet-incapable hosts attached to directly-connected IP subnets. The directly connected subnet having subnet-incapable hosts must use ARP for this feature to be useful.

The way ARP subnet routing works is as follows. When a subnet-incapable host wants to send an IP packet to a destination on a remote subnet, it does not realize that it should send the packet to a router. The subnet-incapable host therefore simply broadcasts an ARP request. The router receives the ARP request and responds as the destination (hence the name proxy) if both arp-subnet-routing is enabled and if the next hop to the destination is over a different interface than the interface receiving the ARP request.

If there are no hosts on your LAN that are subnet-incapable, do not enable ARP-subnet routing. If a LAN needs ARP subnet routing, enable it on all routers on that LAN.

Example: enable arp-subnet-routing

bootp-forwarding

Turns on BOOTP packet forwarding. In order to use the BOOTP forwarding, you must also add one or more BOOTP servers with the add bootp-server command.

Example: enable bootp-forwarding

Maximum number of forwarding hops [4]?
Minimum seconds before forwarding [0]?
Maximum number of forwarding hops

 Maximum number of allowable BOOTP agents that can forward a BOOTP request from the client to the server (this is not the maximum number of IP hops to the server). The default is 4.

Minimum seconds before forwarding

 This parameter is generally not used. Use this parameter when there is a redundant path between the client and the server, and you want to use the secondary path(s) as a standby.

directed-broadcast

Enables the forwarding of IP packets whose destination is a non-local (remote LAN) broadcast address. The source host originates the packet as a unicast and forwards it to a destination subnet where it is exploded into a broadcast.

These packets can be used to locate network servers. This command enables both the forwarding and exploding of directed broadcasts. The IP packet forwarder never forwards link level broadcasts/multicasts unless they correspond to Class D IP addresses. The default setting is enabled.

Note: Forwarding and exploding cannot be implemented separately. Also, the router does not forward subnet-wide IP broadcasts.

Example: enable directed-broadcast

ip-source-routing

Enabling IP source routing causes IP to include forwarding instructions for IP packet in the packet itself. Enabling IP source routing can pose a security risk because an attacker could learn information about your network. The default is disabled.

Example: enable ip-source-routing

per-packet-multipath

If per-packet-multipath is enabled, and there are multiple equal-cost paths to a destination, the router chooses the path for forwarding each packet in a round-robin fashion. The default is disabled.

Example: enable per-packet-multipath

rfc925-routing

Turns on RFC 925 routing. When enabled, the router replies by proxy to all ARP requests for remote destinations that are best reached through the router. Use this command when there are hosts on the LAN that ARP for all destinations, instead of (as is proper) only local destinations.

Example: enable rfc925-routing

udp-forwarding port#

Allows the router to forward UDP broadcast frames for UDP ports that you configured using the add udp-destination command. See Configuring UDP Broadcast Forwarding.

Example: enable udp-forwarding

For which UDP port number [-1]? 36

Exit [C] [M]

Use the exit command to return to the previous prompt level.

Syntax: exit

Example: exit

Filters [C] [M]

From the IP config> prompt, displays the IP Filters Config> prompt.

From the IP> prompt, displays the IP Filters> prompt.

See Using IP Filters for information on IP filtering.

Hostnames [M]

Displays the hostnames and IP addresses that you added using the add hostname command.

Example: hostnames

Interface Addresses [M]

Displays the router's IP interface addresses together with their corresponding hardware interface and IP address mask.

IP does not use hardware interfaces that do not have configured IP interface addresses; they are listed as Not an IN net. There is one exception. Serial interfaces do not need an assigned IP interface addresses to forward IP traffic. Such serial lines are called unnumbered. They show up as having address 0.0.0.0.

Syntax: interface

Example: interface

 Interface  IP Address(es)   Mask(s)
   Eth/0   128.185.227.22  255.255.255.0
   PPP/0   162.9.0.22      255.255.0.0
   PPP/1   0.0.0.0         0.0.0.0
Interface

 Hardware type of the interface.

IP addresses

 IP address of the interface.

Mask

 Subnet mask of the interface.

List [C]

Displays various pieces of the IP configuration.

Syntax: list

all
addresses
bootp
hostname
protocols
routes
sizes
tags
udp-forwarding

all

 Prints the entire IP configuration.

Example: list all

addresses

Lists the IP addresses that are assigned to the router's interfaces, including whether the address is numbered, unnumbered, or dynamic.

Example: list addresses

bootp

Indicates whether BOOTP forwarding is enabled or disabled, as well as the configured list of BOOTP servers.

Example: list bootp

hostname

Displays the hostnames and IP addresses that you added using the add hostname command.

Example: list hostname

protocols

Prints the configured state of the IP routing protocols along with whether ARP subnet routing is enabled or disabled.

Example: list protocols

routes

Prints the list of configured static network/subnet routes. Also lists any configured default gateways.

Example: list routes

sizes

Displays the routing table size, re-assembly buffer size, and the route cache size.

Example: list sizes

tags

Displays the per-interface tags that are associated with received RIP information. These tags can be used to group routes together for later re-advertisement via EGP where a tag is treated as if it were a route's source AS.

Example: list tags

udp-forwarding

Displays the UDP broadcast configuration. See Configuring UDP Broadcast Forwarding.

Example: list udp-forwarding

UDP broadcast forwarding is enabled for the following UDP port numbers:
   36
UDP broadcast forwarding destinations:
   Port   Destination
   36     20.1.2.2

NAT [C] [M]

 From the IP config> prompt, displays the NAT Config> prompt.

From the IP> prompt, displays the NAT> prompt.

See Using IP Network Address Translation (NAT).

Syntax: nat

Example: nat

Network Address Translation Configuration

NAT Config>

Ping [M]

Causes the router to send ICMP Echo Requests to a destination once a second and watch for a response. You can use ping to isolate trouble in an internetwork environment.

This process is done continuously, incrementing the ICMP sequence number with each additional packet. Matching received ICMP Echo responses are reported with their sequence number and the round trip time. The granularity (time resolution) of the round trip time calculation is usually (depending on platform) on the order of 20 milliseconds. The ping command completes when you type a character in the monitoring process. At that time, a summary of packet loss, round trip time, and number of ICMP destination unreachables received is displayed.

When a multicast address is given as destination, there may be multiple responses printed for each packet sent, one for each group member. Each returned response is displayed with the source address of the responder.

Note: The size of the ping (number of data bytes in the ICMP message, excluding the ICMP header) is 56 bytes, and the TTL used is 60.

Syntax: ping interface-address

 Example: ping 128.185.142.11

PING 128.185.142.11: 56 data bytes
64 bytes from 128.185.142.11: icmp_seq=0. time=0. ms
64 bytes from 128.185.142.11: icmp_seq=1. time=0. ms
64 bytes from 128.185.142.11: icmp_seq=2. time=0. ms
64 bytes from 128.185.142.11: icmp_seq=3. time=0. ms
64 bytes from 128.185.142.11: icmp_seq=4. time=0. ms
64 bytes from 128.185.142.11: icmp_seq=5. time=0. ms

----128.185.142.11 PING Statistics----
6 packets transmitted, 6 packets received, 0% packet loss
round-trip (ms)  min/avg/max = 0/0/0

RIP [C] [M]

 From the IP config> prompt, displays the RIP Config> prompt.

From the IP> prompt, displays the RIP> prompt.

See Using RIPv1, RIPv2, and Triggered RIP.

Syntax: rip

Example: rip

RIP config>

Route [M]

Displays the route (if one exists) to a IP destination. If a route exists, the IP address(es) of the next hop(s) is displayed, along with detailed information concerning the matching routing table entry. (See the IP dump command.)

Syntax: route ip-destination

Example: route 18.10.0.5

Destination:       18.10.0.5
Mask:              255.0.0.0
Route type:        SPE1
Distance:          3
Age:               1
Next hop(s):       128.185.123.18    (PPP/0)
Example: route 128.185.230.0

Destination:       128.185.230.0
Mask:              55.255.255.0
Route type:        SPF
Distance:          1
Age:               1
Next hop(s):       128.185.230.0    (TKR/0)
Example: route 128.185.232.0

Destination:       128.185.232.0
Mask:              255.255.255.0
Route type:        RIP
Distance:          3
Age:               0
Next hop(s):       128.185.146.4   (Eth/0)

Set [C]

Sets certain values, routes, and formats within your IP configuration.

Syntax: set

cache-size
default network-gateway
default subnet-gateway
internal-ip-address
reassembly-size
router-id
routing table-size
tag

cache-size entries

 Configures the maximum number entries for the IP routing cache. Default: 64. Maximum: none.

Example: set cache-size 

number of cache entries [64]?

default network-gateway next-hop cost

 Configures a route to the authoritative router (default gateway). You should assume that the router's default gateway has more complete routing information than the router itself.

The route is specified by the IP address of the next hop (next-hop) and the distance (cost) to the default gateway.

All packets having unknown destinations are forwarded to the authoritative router (default gateway).

Example: set default network-gateway

Default gateway [0.0.0.0]? 192.9.1.10
gateway's cost [1]? 10

default subnet-gateway subnetted-network next-hop cost

 Configures a route to a subnetted network's authoritative router (default subnet gateway). You can configure a separate default subnet gateway for each subnetted network.

The IP address of the next hop (next-hop) and the distance (cost) to the default subnet gateway specify the route.

All packets destined for unknown subnets of a known subnetted network are forwarded to the subnetted network's default subnet gateway.

Example: set default subnet-gateway

For which subnetted network [0.0.0.0]? 128.0.0.0
Default gateway [0.0.0.0]? 128.185.123.22
gateway's cost [1]? 6

internal-IP-address

 Sets the internal IP address that belongs to the router as a whole, and not any particular interface. This address is always reachable regardless of the state of the interface. When the internal IP address and the router ID are set in the same router, the internal IP address has precedence over the router ID. To delete the internal IP address set the address to 0.0.0.0.

Example: set internal-ip-address 

Internal IP address [0.0.0.0]? 142.82.10.1

reassembly-size

 Configures the size of the buffers that are used to re-assemble fragmented IP packets. The range is 2048 to 65535. The default is 12000.

Note: This parameter is relevant to the EGP routing protocol.

Example: set reassembly-size

Reassembly buffer size [12000]?

router-id ip-address

 Sets the default IP address the router uses when sourcing various kinds of IP traffic. This address is of particular importance in multicasting. For a definition of router ID, see Router ID.

The router ID must match one of the configured IP interface addresses of the router. If not, it is ignored. When ignored, or just not configured, the default IP address of the router is set to the first IP address in the router's configuration.

Note: Setting a router ID may cause the router's OSPF router ID to change. If this happens, link state advertisements originated by the router before the router ID change persist until they age out, possibly as long as 30 minutes. This can cause an increase in link state database size.

Example: set router-id

Router-ID [0.0.0.0]? 128.185.120.209

routing table-size number-of-entries

 Sets the size of the router's IP routing table. The default is 768 entries. Setting the routing table size too small causes dynamic routing information to be discarded. Setting the routing table size too large wastes router memory resources.

Example: set routing table-size

number of nets [768]? 1000

tag

 Configures the per-interface tags associated with received RIP information. These tags can be used to group routes together for later re-advertisement via EGP where a tag is treated as if it were a route's source AS. (See the IP add output-exchange command.) Tags are also propagated by the OSPF routing protocol.

Example: set tag

Interface address [0.0.0.0]?
Interface tag (AS number) [0]?

Sizes [M]

Displays the configured sizes of specific IP parameters.

Syntax: sizes

Example: sizes

        Routing table size:             768
        Table entries used:             69
        Reassembly buffer size:         12000
        Largest reassembled pkt:        0
        Size of routing cache:          64
        # cache entries in use:         0
Routing table size

 Number of entries that the routing table maintains.

Table entries used

 Number of entries used from the routing table

Reassembly buffer size

 Configured size of the re-assembly buffer that is used to re-assemble fragmented IP packets.

Largest reassembled pkt

 Largest IP packet that this router has re-assembled.

Size of routing cache

 Configured the size of the routing cache.

# of cache entries in use

 Number of entries currently being used from the cache.

Static Routes [M]

Displays the list of configured static routes, configured default gateways, and default subnet gateways.

Each static route's destination is specified by an address-mask pair. Default gateways appear as static routes to destination 0.0.0.0 with mask 0.0.0.0. Default subnet gateways also appear as static routes to the entire IP subnetted network.

The example below shows a configured default gateway, a configured default subnet gateway (assuming 128.185.0.0 is subnetted), and a static route to network 192.9.10.0.

Syntax: static

Example: static

Net             Mask            Cost  Next hop
0.0.0.0         0.0.0.0         1     128.185.123.18
128.185.0.0     255.255.0.0     1     128.185.123.22
192.9.10.0      255.255.255.0   10    128.185.123.22
Net

 Network address of the route.

Mask

 Subnet mask of the IP address.

Cost

 Cost of using this route.

Next Hop

 Next router a packet would pass through using this route.

Traceroute [M]

Displays the entire path to a destination, hop by hop. For each successive hop, traceroute sends out three probes, and displays the IP address of the responder, together with the round trip time associated with the response. If a particular probe receives no response, the software displays an asterisk. Each line in the display relates to the set of three probes, with the left most number indicating the distance from the router sending the command (in router hops).

A traceroute is complete whenever the destination is reached, an ICMP Destination Unreachable is received, or the path length reaches 32 router hops.

When a probe receives an unexpected result, the software can display several indications:
!N

 An ICMP Destination Unreachable (net unreachable) was received.

!H

 An ICMP Destination Unreachable (host unreachable) was received.

!P

 An ICMP Destination Unreachable (protocol unreachable) was received; since the probe is a UDP packet sent to a strange port, a port unreachable is what we expect.

!

 The destination was reached, but the reply that the destination sent was received with a TTL of 1. This usually indicates an error in the destination, prevalent in some versions of UNIX, whereby the destination inserts the probe's TTL in its replies. This unfortunately leads to a number of lines consisting solely of asterisks before the destination is finally reached.

Syntax: traceroute interface-address

Example: traceroute 128.185.142.239

TRACEROUTE 128.185.124.110: 56 data bytes
 1 128.185.142.7 16 ms 0 ms 0 ms
 2 128.185.123.22 16 ms 0 ms 16 ms
 3 * * *
 4 * * *
 5 128.185.124.110 16 ms ! 0 ms ! 0 ms !
TRACEROUTE

 Displays the destination address and the size of the packet being sent to that address.

1

 The first trace showing the destination's NSAP and the amount of time it took the packet to arrive at the destination. The packet is traced three times.

Destination
unreachable

 No route to destination is available.

1 * * *
2 * * *

 The router expects some form of response from the destination, but the destination is not responding.

UDP-Forward [M]

Displays the UDP broadcast ports and addresses that you added using add udp-destination.

Syntax: udp-forward

Example: udp-forward

UDP Port   IP Address
    35      20.2.1.1
    20      22.2.1.2

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