C H A P T E R 2

IP

IP is an identifier for a computer or device on a TCP/IP network. Networks using the TCP/IP protocol route messages based on the IP address of the destination. The format of an IP address is a 32-bit numeric address written as four numbers separated by periods. Each number can be zero to 255, for example 10.5.25.180.

Every computer that communicates over the Internet is assigned an IP address that uniquely identifies the device and distinguishes it from other computers. Within an isolated network, IP addresses can be assigned at random as long as each one is unique. However, to connect a private network to the Internet, registered IP addresses must be used (called Internet addresses) to avoid duplicates. The four numbers in an IP address are used in different ways to identify a particular network and a host on that network.

Four regional Internet registries--ARIN, RIPE NCC, LACNIC and APNIC--assign Internet addresses from the following three classes.

- Class A. Supports 16 million hosts on each of 126 networks

- Class B. Supports 65,000 hosts on each of 16,000 networks

- Class C. Supports 254 hosts on each of 2 million networks

The number of unassigned Internet addresses is running out, so a new classless scheme called CIDR is gradually replacing the system based on classes A, B, and C.

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2.1 IP Commands

The following SEFOS commands are available for the IPv4 module:

- ip redirects / ip icmp redirects

- ip unreachables

- ip mask-reply

- ip echo-reply

- maximum-paths

- ip rarp client request

- ip aggregate-route

- traffic-share

- ip path mtu discover

- ip path mtu

- ip rarp client

- ip directed-broadcast

- show ip rarp

- show ip pmtu

- ping ip-address

- ip route

- ip routing

- ip default-ttl

- arp timeout

- arp ip-address

- ip arp max-retries

- show ip traffic

- show ip route

- show ip arp

- show ip information

### 2.1.1 `ip redirects`

Enables sending ICMP redirect messages. The `no` form of the command disables sending ICMP redirect messages.

    ip redirects

    no ip redirects

Mode | Global Configuration
Defaults | Sending of ICMP redirect messages is enabled.
Example | `SEFOS(config)#` ip redirects
Notes | The router may send an ICMP redirect message to the originator of the packet, when the packet enters an IP interface and exits the same interface. This message notifies the originator that there is a better gateway for the assigned destination address.

#### Related Commands

show ip information - Displays IP configuration information

### 2.1.2 `ip icmp redirects`

Enables sending ICMP redirect messages. The `no` form of the command disables sending ICMP redirect messages.

    ip icmp redirects {host | subnet}

    no ip icmp redirects

Syntax Description | host - Sends ICMP host redirect messages. subnet - Sends ICMP subnet redirect messages.
Mode | Global Configuration
Defaults | Sending of ICMP redirect messages is enabled.
Example | `SEFOS(config)#` ip redirects
Notes | The router may send an ICMP redirect message to the originator of the packet, when the packet enters an IP interface and exits the same interface. This message notifies the originator that there is a better gateway for the assigned destination address.

### 2.1.3 `ip unreachables`

Enables sending ICMP unreachable message. The `no` form of the command disables sending ICMP unreachable messages.

    ip unreachables

    no ip unreachables

Mode | Global Configuration
Defaults | Enabled
Example | `SEFOS(config)#` ip unreachables
Notes | This command enables the router to send an ICMP unreachable message to the source if the router receives a packet that has an unrecognized protocol or no route to the destination address. ICMP provides a mechanism that enables a router or destination host to report an error in data traffic processing to the original source of the packet. ICMP messages provide feedback about problems that occur in the communication environment.

#### Related Commands

show ip information - Displays IP configuration information

### 2.1.4 `ip mask-reply`

Enables sending ICMP mask-reply messages. The `no` form of the command disables sending ICMP mask-reply messages.

    ip mask-reply

    no ip mask-reply

Mode | Global Configuration
Defaults | Enabled
Example | `SEFOS(config)#` ip mask-reply
Notes | ICMP is an extension to the Internet Protocol (IP) defined by RFC 792. ICMP supports packets containing error, control, and informational messages. The `ping` command, for example, uses ICMP to test an internet connection. Hosts can find subnet masks by sending an Internet Control Message Protocol (ICMP) mask request message. Routers respond to this request with an ICMP mask reply message. A gateway receiving an address mask request must return it with the address mask field set to the 32-bit mask of the bits identifying the subnet and network.

#### Related Commands

show ip information - Displays IP configuration information

### 2.1.5 `ip echo-reply`

Enables sending ICMP echo reply messages. The `no` form of the command disables sending ICMP echo reply messages.

    ip echo-reply

    no ip echo-reply

Mode | Global Configuration
Defaults | Enabled.
Example | `SEFOS(config)#` ip echo-reply
Notes | ICMP echo messages are sent to a remote host and are returned in an echo-reply response. The primary use of these messages is to check the availability of the target machine.

#### Related Commands

show ip information - Displays IP configuration information

### 2.1.6 `maximum-paths`

Sets the maximum number of multipaths. The `no` form of the command sets the maximum number of multipaths to its default value.

    maximum-paths 1-16

    no maximum-paths

Mode | Global Configuration
Defaults | 2
Example | `SEFOS(config)#` maximum-paths 3
Notes | This configuration is not saved and thus will not be effective once the switch is restarted.

#### Related Commands

show ip information - Displays IP configuration information

### 2.1.7 `ip rarp client request`

Sets the number of RARP client request retries or interval between requests. The `no` form of the command sets the RARP client request retries or interval between retries to their default values.

    ip rarp client request {interval 30-3000 | retries 2-10}

    no ip rarp client request {interval | retries}

Syntax Description | interval - The interval (in seconds) after which an unanswered RARP request is transmitted. retries - The maximum number of retransmissions of RARP request packets.
Mode | Global Configuration
Defaults | 2
Example | `SEFOS(config)#` ip rarp client request interval 30
Notes | Reverse Address Resolution Protocol (RARP) is used for diskless computers to determine their IP address using the network. RARP provides the opposite service to ARP in that it is used only when the Ethernet address is known and the IP address is needed. RARP requests are most commonly sent by diskless clients and JumpStart clients during bootup. The client uses the RARP protocol to broadcast the Ethernet address and asks for the corresponding IP address.

#### Related Commands

show ip rarp - Displays RARP configuration information

### 2.1.8 `ip aggregate-route`

Sets the maximum number of aggregate routes. The `no` form of the command sets the maximum number of aggregate routes to its default value.

    ip aggregate-route 5-4095

    no ip aggregate-route

Mode | Global Configuration
Defaults | 10
Example | `SEFOS(config)#` ip aggregate-route 5
Notes | This command takes effect only after the configuration is saved and the router is restarted.

#### Related Commands

show ip information - Displays IP configuration information

### 2.1.9 `traffic-share`

Enables traffic sharing (load sharing of IP packets). Traffic sharing finds routes with the least cost to evenly distrubute load. EIGRP provides intelligent traffic sharing.

Traffic sharing is controlled by selecting the mode of distribution. Traffic-sharing balances and distributes traffic proportionately to the ratio of metrics of different routes.

The `no` form of this command disables traffic sharing.

    traffic-share

    no traffic-share

Mode | Global Configuration
Defaults | Load sharing is disabled.
Example | `SEFOS(config)#` traffic-share

#### Related Commands

show ip information - Displays IP configuration information

### 2.1.10 `ip path mtu discover`

Enables path MTU discovery. The `no` form of the command disables path MTU discovery.

    ip path mtu discover

    no ip path mtu discover

Mode | Global Configuration
Defaults | Disabled
Example | `SEFOS(config)#` ip path mtu discover
Notes | Overrides the route-based and application-level requests. When disabled, the MTU path is not discovered when requested by an application.

#### Related Commands

show ip information - Displays IP configuration information

### 2.1.11 `ip path mtu`

Sets the MTU for usage in PMTU discovery. The `no` form of the command removes MTU in PMTU discovery.

    ip path mtu dest-ip-addr type-of-service 68-65535

    no ip path mtu dest-ip-addr type-of-service

Syntax Description | dest-ip-addr - Destination IP address. type-of-service - Type of service of the configured route. 68-65535 - Maximum transmission unit.
Mode | Global Configuration
Defaults | type-of-service - 0
Example | `SEFOS(config)#` ip path mtu 10.0.0.1 0 1800
Notes | Path MTU discovery must be enabled to execute this command.

#### Related Commands

- ip path mtu discover - Enables PMTU discovery

- show ip pmtu - Displays the configured PMTU entries

### 2.1.12 `ip rarp client`

Enables RARP client. The `no` form of the command disables RARP client.

    ip rarp client

    no ip rarp client

Mode | Interface Configuration
Defaults | Enabled
Example | `SEFOS(config-if)#` ip rarp client
Notes | When the IP address configuration mode is dynamic, the IP address of the default interface is obtained through RARP. The RARP server is disabled when the RARP client is enabled.

#### Related Commands

show interfaces - Displays all the interface details

show ip rarp - Displays RARP configuration information

### 2.1.13 `ip directed-broadcast`

Enables forwarding of directed broadcasts. The IP directed broadcast is an IP packet with a destination that has a valid IP subnet address, but the source is from a node outside the destination subnet. The routers from outside the subnet forward the IP directed broadcast like any other IP packet.

When the directed packets reach a router in the destination subnet, the packet is exploded as a broadcast in the subnet. The header information on the broadcast packet is rewritten for the broadcast address in the subnet. The packet is sent as link-layer broadcast.

The `no` form of this command disables forwarding of directed broadcasts.

    ip directed-broadcast

    no ip directed-broadcast

Mode | Interface Configuration
Defaults | Disabled
Example | `SEFOS(config-if)#` ip directed-broadcast
Notes | Broadcasts a message to the particular subnet that the host belongs.

#### Related Commands

show interfaces - Displays the interface status and configuration

### 2.1.14 `show ip rarp`

Displays RARP configuration information.

    show ip rarp

Mode | Privileged EXEC
Example | `SEFOS#` show ip rarp RARP Configurations: -------------------- Maximum number of RARP request retransmission retries is 4 RARP request retransmission timeout is 100 seconds RARP Statistics: ---------------- 0 responses discarded

#### Related Commands

ip rarp client request - Sets the number of RARP client request retries

ip rarp client - Enables RARP client

### 2.1.15 `show ip pmtu`

Displays the configured PMTU entries.

    show ip pmtu

Mode | Privileged EXEC
Example | `SEFOS#` show ip pmtu Ip Path MTU Table ----------------- Destination TOS PMTU 10.0.0.1 0 1800

#### Related Commands

ip path mtu - Sets the MTU for usage in PMTUD

### 2.1.16 `ping` ip-address

Sends echo messages.

    ping [ ip ] address [{repeat|count} packet_count(1-10)] [size packet_size(36-2080)] [source { ip-address | vlan short(1-4094) } ] [timeout time_out(1-100)]

Syntax Description | ip-address - IP address of the node to be pinged. size - Size of the data portion of the `ping` PDU. This value ranges between 36 and 2080. count - Number of times the given node address is to be pinged. This value ranges between 1 and 10. timeout - Time in seconds after which the entity waiting for the `ping` response times out. This value ranges between 1 and 100 seconds.
Mode | User EXEC
Defaults | size packet_size - 40 count packet_count - 3 timeout - 1
Example | `SEFOS(config)#` ping 10.0.0.2 Reply Received From :10.0.0.2, TimeTaken : 20 msecs Reply Received From :10.0.0.2, TimeTaken : 10 msecs Reply Received From :10.0.0.2, TimeTaken : 10 msecs --- 10.0.0.2 Ping Statistics --- 3 Packets Transmitted, 3 Packets Received, 0% Packets Loss

### 2.1.17 `ip route`

Adds a static route. The `no` form of the command deletes a static route. By default, no static routes are created.

    ip route prefix mask {next-hop | Vlan 1-4094 | interface-type interface-id Cpu0} private

    no ip route prefix mask {next-hop | Vlan 1-4094 | interface-type interface-id Cpu0} private

Syntax Description | prefix - IP route prefix for the destination (destination IP address). mask - Subnet mask for the destination. next-hop - IP address or IP alias of the next hop that can be used to reach that network. You can add the route of the next hop only if the next hop network is accessible from SEFOS. Vlan - VLAN identifier (1-0494). interface-type - Interface type. interface-id - Interface identifier. Cpu0 - Out of band management interface. private - Private route.
Mode | Global Configuration
Defaults | Distance - 1
Example | `SEFOS(config)#` ip route 192.168.0.0 255.255.0.0 Vlan 1 private
Notes | When the next-hop object is unknown or not relevant, its value must be set to zero. Interface must be a router port. The IP address that you enter must match the subnet mask. In other words, if the IP address that you enter is 192.168.0.0, then the mask must be 255.255.0.0. The `no ip route` command used with the private option (for example, `no ip route 192.168.0.0 255.255.0.0 Vlan 1 private`) will resets the private flag in the routing entry. This command does not remove the route. To remove the route, run the `no ip route` command without the `private` option. When you are adding a static route, you might see the error message “`Nexthop name, Permanent options are not supported.`" Disregard this message. The static route will continue to be added.

#### Related Commands

show ip route - Displays the IP routing table

### 2.1.18 `ip routing`

Enables IP routing. The `no` form of the command disables IP routing.

    ip routing

    no ip routing

Mode | Global Configuration
Defaults | Enabled.
Example | `SEFOS(config)#` ip routing
Notes | A static route is appropriate when SEFOS cannot dynamically build a route to the destination.

#### Related Commands

- show ip information - Displays IP configuration information

- show ip route - Displays the IP routing table

### 2.1.19 `ip default-ttl`

Sets the TTL value. The `no` form of the command sets the TTL to the default value.

    ip default-ttl 1-255

    no ip default-ttl

Mode | Global Configuration
Defaults | 64 seconds.
Example | `SEFOS(config)#` ip default-ttl 1
Notes | TTL is a value in an IP packet that tells a network router whether or not the packet has been in the network too long and must be discarded. The default Windows 95/98 TTL value is 32 seconds.

#### Related Commands

show ip information - Displays IP configuration information

### 2.1.20 `arp timeout`

Sets the ARP cache timeout. The `no` form of the command sets the ARP cache timeout to its default value.

    arp timeout 30-86400

    no arp timeout

Mode | Global Configuration
Defaults | 300 (seconds)
Example | `SEFOS(config)#` arp timeout 35

#### Related Commands

show ip arp - Displays IP ARP table for the given VLAN ID, IP Address of ARP entry, MAC Address of ARP entry, IP ARP summary table, ARP configuration information.

### 2.1.21 `arp` ip-address

Adds a static entry in the ARP cache. The `no` form of the command deletes a static entry from the ARP cache.

    arp ip-address hardware-address {Vlan 1-4094 | interface-type interface-id | Cpu0}

    no arp ip-address

Syntax Description | ip-address - IP address or IP alias to map to the specified MAC address. hardware-addr - MAC address to map to the specified IP address or IP alias. Vlan - VLAN identifier (1-4094). Cpu0 - Out-of-band management interface. interface-type - Interface type. interface-id - Interface identifier.
Mode | Global Configuration
Example | `SEFOS(config)#` arp 10.203.120.21 00:11:22:33:44:55 Vlan 1
Notes | ARP is a protocol used by IP, specifically IPv4, to map IP network addresses to the hardware addresses used by a data link protocol. The phrase address resolution refers to the process of finding an address of a computer in a network.

#### Related Commands

show ip arp - Displays IP ARP table for the given VLAN ID, IP Address of ARP entry, MAC Address of ARP entry, IP ARP summary table, ARP configuration information.

### 2.1.22 `ip arp max-retries`

Sets the maximum number of ARP request retries. The no form of the command sets the maximum number of ARP request retries to its default value.

    ip arp max-retries 2-10

    no ip arp max-retries

Mode | Global Configuration
Defaults | 3
Example | `SEFOS(config)#` ip arp max-retries 2
Notes | Configures the maximum number of ARP requests that the switch generates before deleting an unresolved ARP entry.

#### Related Commands

show ip arp - Displays IP ARP table for the given VLAN ID, IP Address of ARP entry, MAC Address of ARP entry, IP ARP summary table, ARP configuration information.

### 2.1.23 `show ip traffic`

Displays the IP protocol statistics.

    show ip traffic [interface {Vlan 1-4094 | tunnel 1-128 | interface-type interface-id hc}

Syntax Description | Vlan - VLAN identifier (1-4094). tunnel - tunnel identifier (1-128). interface-type - Interface type. interface-ID - Interface identifier. hc - High counters.
Mode | Privileged EXEC
Example | `SEFOS#` show ip traffic IP Statistics ____________________ Rcvd: 0 total, 0 header error discards 0 bad ip address discards, 0 unsupported protocol discards Frags: 0 reassembled, 30 timeouts, 0 needs reassembly 0 fragmented, 0 couldn’t fragment Bcast: Sent: 0 forwarded, 0 generated requests Drop: 0 InDiscards 0 InDelivers 0 InMcastPkts 0 InTruncated 0 InOctets 0 InNoRoutes 0 ReasmFails 0 InMcast Octets 0 InBcastPkts 0 OutDiscards 0 OutMcastPkts 0 OutFrgCreates 0 OutForwDgrms 0 OutTrnsmits 0 OutFrgRqds 0 OutOctets 0 OutMcstOctets 0 OutBcstPkts 0 DiscntTime 1000 RefrshRate

### 2.1.24 `show ip route`

Displays the IP routing table.

    show ip route [ {ip-address mask | connected | ospf | rip | static | summary}]

Syntax Description | ip-address - Destination IP address. mask - Prefix mask for the destination. connected - Directly connected network routes. ospf -OSPF. rip - RIP. static - Static routes. summary - Summary of all routes.
Mode | Privileged EXEC
Example | `SEFOS#` show ip route `` `S 20.0.0.0/8 [1] via 100.20.6.20` `S 30.0.0.0/8 [4] via 120.20.6.20` `S 40.0.0.0/8 is directly connected, vlan1` `S 50.0.0.0/8 [1] via 100.20.6.21` `C 100.0.0.0/8 is directly connected, vlan1` `C 110.0.0.0/8 is directly connected, vlan2` `C 120.0.0.0/8 is directly connected, vlan3` `` `SEFOS#` show ip route 20.0.0.0 `` `Codes: C - connected, S - static, R - RIP, O - OSPF` `S 20.0.0.0/8 [1] via 100.20.6.20` `` `SEFOS#` show ip route 30.0.0.0 255.0.0.0 `` `Codes: C - connected, S - static, R - RIP, O - OSPF` `S 30.0.0.0/8 [4] via 120.20.6.20`

#### Related Commands

- ip route - Adds a static route

- ip routing - Enables IP routing

### 2.1.25 `show ip arp`

Displays IP ARP table.

    show ip arp [{Vlan 1-4094 | interface-type interface-id | ip-address | mac-address | summary | information}]

Syntax Description | Vlan - VLAN ID (1-4094). interface-type - Interface type. interface-ID - Interface identifier. ip-address - IP address of ARP entry. mac-address - MAC address of ARP entry. summary - IP ARP table summary. information - ARP configuration information.
Mode | Privileged EXEC
Example | `SEFOS#` show ip arp Address Hardware Address Type Interface Mapping ------- ---------------- ---- --------- ------- 110.20.6.99 00:11:22:44:55:66 ARPA vlan1 Static 100.20.6.99 00:11:22:33:44:55 ARPA vlan2 Static 110.20.6.101 00:5e:01:00:11:55 ARPA vlan2 Static SEFOS# show ip arp vlan 1 Address Hardware Address Type Interface Mapping ----------- ---------------- ---- --------- ------- 110.20.6.99 00:11:22:44:55:66 ARPA vlan1 Static SEFOS# show ip arp 00:10:b5:66:a7:0e Address Hardware Address Type Interface Mapping ------- ---------------- ---- --------- ------- 100.20.6.20 00:10:b5:66:a7:0e ARPA vlan1 Dynamic SEFOS# show ip arp 100.20.6.99 Address Hardware Address Type Interface Mapping ----------- ---------------- ---- --------- ------- 100.20.6.99 00:11:22:33:44:55 ARPA vlan2 Static SEFOS# show ip arp summary 3 IP ARP entries, with 0 of them incomplete SEFOS# show ip arp information ARP Configurations: ------------------- Maximum number of ARP request retries is 10 ARP cache timeout is 7200 seconds

#### Related Commands

- arp timeout - Sets the ARP cache timeout

- ip arp max-retries - Sets the maximum number of ARP request retries

### 2.1.26 `show ip information`

Displays IP configuration information.

    show ip information

Mode | Privileged EXEC
Example | `SEFOS#` show ip information Global IP Configuration: ________________________ IP routing is enabled Default TTL is 64 ICMP redirects are always sent ICMP unreachables are always sent ICMP echo replies are always sent ICMP mask replies are always sent Number of aggregate routes is 10 Number of multi-paths is 2 Load sharing is disabled Path MTU discovery is disabled

#### Related Commands

- ip redirects / ip icmp redirects - Enables sending ICMP

- ip unreachables - Enables sending ICMP unreachable message

- ip mask-reply - Enables sending ICMP mask reply messages

- ip echo-reply - Enables sending ICMP echo reply messages

- maximum-paths - Sets the maximum number of multipaths

- ip aggregate-route - Sets the maximum number of aggregate routes

- ip path mtu discover - Enables PMTU discovery

- traffic-share - Enables traffic sharing

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