IP Routing Features


The switch offers the following IP routing features:

IP Static routes

Up to 256 static routes

RIP (Router Information Protocol)

Supports RIP Version 1, Version 1 compatible with Version 2 (default), and Version 2

IRDP (ICMP Router Discovery Protocol)

Advertises the IP addresses of the routing interfaces on this switch to directly attached host systems

DHCP Relay

Allows you to extend the service range of your DHCP server beyond its single local network segment

Throughout this chapter, the switches are referred to as "routing switches." When IP routing is enabled on your switch, it behaves just like any other IP router.

Basic IP routing configuration consists of adding IP addresses, enabling IP routing, and enabling a route exchange protocol, such as RIP.

For configuring the IP addresses, see the chapter "Configuring IP Addresses" in the Management and Configuration Guide for your switch. Use the information in this chapter if you need to change some of the IP parameters from their default values or if you want to view configuration information or statistics.

IP interfaces

On the routing switches, IP addresses are associated with individual VLANs. By default, there is a single VLAN (Default_VLAN) on the routing switch. In that configuration, a single IP address serves as the management access address for the entire device. If routing is enabled on the routing switch, the IP address on the single VLAN also acts as the routing interface.

Each IP address on a routing switch must be in a different subnet. You can have only one VLAN interface in a given subnet. For example, you can configure IP addresses and on the same routing switch, but you cannot configure and on the same routing switch.

You can configure multiple IP addresses on the same VLAN.

The number of IP addresses you can configure on an individual VLAN interface is 32.

You can use any of the IP addresses you configure on the routing switch for Telnet, Web management, or SNMP access, as well as for routing.

[NOTE: ]

NOTE: All HP devices support configuration and display of IP address in classical subnet format (example: and Classless Interdomain Routing (CIDR) format (example: You can use either format when configuring IP address information. IP addresses are displayed in classical subnet format only.

IP tables and caches

ARP cache table

The ARP cache contains entries that map IP addresses to MAC addresses. Generally, the entries are for devices that are directly attached to the routing switch.

An exception is an ARP entry for an interface-based static route that goes to a destination that is one or more router hops away. For this type of entry, the MAC address is either the destination device's MAC address or the MAC address of the router interface that answered an ARP request on behalf of the device, using proxy ARP.

ARP cache

The ARP cache contains dynamic (learned) entries. The software places a dynamic entry in the ARP cache when the routing switch learns a device's MAC address from an ARP request or ARP reply from the device.

The software can learn an entry when the switch or routing switch receives an ARP request from another IP forwarding device or an ARP reply. Here is an example of a dynamic entry:

ARP cache dynamic entry

    IP Address      MAC Address      Type       Port
1    0800.5afc.ea21   Dynamic      6

Each entry contains the destination device's IP address and MAC address.

To configure other ARP parameters, see Configuring ARP parameters.

IP route table

The IP route table contains routing paths to IP destinations.

[NOTE: ]

NOTE: The default gateway, which you specify when you configure the basic IP information on the switch, is used only when routing is not enabled on the switch.

Routing paths

The IP route table can receive the routing paths from the following sources:

  • Directly-connected destination, which means there are no router hops to the destination

  • Static IP route, which is a user-configured route

  • Route learned through RIP

Administrative distance

The IP route table contains the best path to a destination. When the software receives paths from more than one of the sources listed above, the software compares the administrative distance of each path and selects the path with the lowest administrative distance. The administrative distance is a protocol-independent value from 1 to 255.

The IP route table is displayed by entering the show ip route command from any context level in the console CLI. Here is an example of an entry in the IP route table:

IP route table entry

Destination    Gateway     VLAN  Type      Sub-Type   Metric   Dist.
-------------- ----------- ----- --------- ---------- -------- ----        connected            1        0

Each IP route table entry contains the destination's IP address and subnet mask and the IP address of the next-hop router interface to the destination. Each entry also indicates route type, and for OSPF routes, the subtype, and the route's IP metric (cost.) The type indicates how the IP route table received the route.

To configure a static IP route, see Configuring a static IP route.

IP forwarding cache

The IP forwarding cache provides a fast-path mechanism for forwarding IP packets. The cache contains entries for IP destinations. When an HP routing switch has completed processing and addressing for a packet and is ready to forward the packet, the device checks the IP forwarding cache for an entry to the packet's destination.

  • If the cache contains an entry with the destination IP address, the device uses the information in the entry to forward the packet out the ports listed in the entry. The destination IP address is the address of the packet's final destination. The port numbers are the ports through which the destination can be reached.

  • If the cache does not contain an entry, the software can create an entry in the forwarding cache.

Each entry in the IP forwarding cache has an age timer. The age interval depends on the number of entries in the table. The age timer ranges from 12 seconds (full table) to 36 seconds (empty table.) Entries are aged only if they are not being used by traffic. If you have an entry that is always being used in hardware, it will never age. If there is no traffic, it will age in 12 to 36 seconds. The age timer is not configurable.

[NOTE: ]

NOTE: You cannot add static entries to the IP forwarding cache.

IP route exchange protocols

The switch supports the RIP IP route exchange protocol.

This protocol provides routes to the IP route table and is disabled by default. For configuration information, see Configuring RIP parameters.

IP global parameters for routing switches

IP global parameters for routing switches lists the IP global parameters and the page where you can find more information about each parameter.

IP global parameters for routing switches

Parameter Description Default See page
Address Resolution Protocol (ARP) A standard IP mechanism that routers use to learn the MAC address of a device on the network. The router sends the IP address of a device in the ARP request and receives the device's MAC address in an ARP reply. Enabled Configuring ARP parameters
ARP age The amount of time the device keeps a MAC address learned through ARP in the device's ARP cache. The device resets the timer to zero each time the ARP entry is refreshed and removes the entry if the timer reaches the ARP age. (Can be set using the menu interface to be as long as 1440 minutes. Go to Menu > Switch Configuration > IP Config.)

See ARP age timer.

Five minutes N/A
Time to Live (TTL) The maximum number of routers (hops) through which a packet can pass before being discarded. Each router decreases a packet's TTL by 1 before forwarding the packet. If decreasing the TTL causes the TTL to be 0, the router drops the packet instead of forwarding it. 64 hops See the chapter "Configuring IP Addressing" in the Management and Configuration Guide.
Directed broadcast forwarding A directed broadcast is a packet containing all ones (or in some cases, all zeros) in the host portion of the destination IP address. When a router forwards such a broadcast, it sends a copy of the packet out each of its enabled IP interfaces.

[NOTE: ]

NOTE: You also can enable or disable this parameter on an individual interface basis. See IP interface parameters — routing switches.

Disabled Enabling forwarding of directed broadcasts
ICMP Router Discovery Protocol (IRDP)

An IP protocol that a router can use to advertise the IP addresses of its router interfaces to directly attached hosts. You can enable or disable the protocol at the Global CLI Config level.

You also can enable or disable IRDP and configure the following protocol parameters on an individual VLAN interface basis at the VLAN Interface CLI Config level.

  • Forwarding method (broadcast or multicast)

  • Hold time

  • Maximum advertisement interval

  • Minimum advertisement interval

  • Router preference level


Configuring IRDP

Enabling IRDP globally

Static route An IP route you place in the IP route table. No entries Static route types
Default network route The router uses the default network route if the IP route table does not contain a route to the destination. Enter an explicit default route ( or as a static route in the IP route table. None configured Configuring the default route

ARP age timer

The ARP age is the amount of time the switch keeps a MAC address learned through ARP in the ARP cache. The switch resets the timer to zero each time the ARP entry is refreshed and removes the entry if the timer reaches the ARP age. For more information on ARP, see IP tables and caches.

You can increase the ARP age timeout maximum to 24 hours or more with this command:


[no] ip arp-age <[1...1440]|infinite>

Allows the ARP age to be set from 1 to 1440 minutes (24 hours.)

If the option infinite is configured, the internal ARP age timeout is set to 99,999,999 seconds (approximately 3.2 years.) An arp-age value of 0 (zero) is stored in the configuration file to indicate that infinite has been configured. This value also displays with the show commands and in the menu display (Menu > Switch Configuration > IP Config.)

Default: 20 minutes

Setting the ARP age timeout to 1000 minutes

HP Switch(config)# ip arp-age 1000

To view the value of ARP age timer, enter the show ip command. The Arp Age time value is shown in bold in The show ip command displaying ARP age.

The show ip command displaying ARP age

HP Switch(config)# show ip

 Internet (IP) Service

  IP Routing : Disabled

  Default Gateway :
  Default TTL     : 64

Arp Age         : 1000
  Domain Suffix   :
  DNS server      :

  VLAN                 | IP Config  IP Address     Subnet Mask      Proxy ARP
  -------------------- + ---------- --------------- --------------- ---------
  DEFAULT_VLAN         | Manual    No

You can also view the value of the ARP age timer in the configuration file. The ip arp-age 1000 value is shown in bold in The ip arp-age value in the running config file.

The ip arp-age value in the running config file

HP Switch(config)# show running-config

Running configuration:

; J9627A Configuration Editor; Created on release #XX.15.XX
; Ver #01:01:00

hostname "Switch"
savepower led
mirror-port 7
stack commander "TEST_STACK"
stack member 1 mac-address 0024A8D13A40

ip arp-age 100
vlan 1
   name "DEFAULT_VLAN"
   untagged 1-28
   ip address dhcp-bootp
vlan 222
   name "VLAN222"
   no ip address
snmp-server community "public" unrestricted
snmp-server host community "public"

You can set or display the arp-age value using the menu interface (Menu > Switch Configuration > IP Config).

The Menu interface displaying the ARP Age value

===========================- TELNET - MANAGER MODE ======================
                  Switch Configuration - Internet (IP) Service

  IP Routing : Disabled

  Default Gateway :
  Default TTL     : 64

Arp Age         : 1000

  IP Config [Manual] : Manual

  IP Address  :
  Subnet Mask :

Actions->    Cancel    Edit    Save    Help

IP interface parameters for routing switches

IP interface parameters — routing switches lists the interface-level IP parameters for routing switches.

IP interface parameters — routing switches

Parameter Description Default See page
IP address A Layer 3 network interface address; separate IP addresses on individual VLAN interfaces. None configured [*]
Metric A numeric cost the router adds to RIP routes learned on the interface. This parameter applies only to RIP routes. 1 (one) Configuring RIP parameters
ICMP Router Discovery Protocol (IRDP) Locally overrides the global IRDP settings. See IP global parameters for routing switches for global IRDP information. Disabled Enabling IRDP globally
IP helper address The IP address of a UDP application server (such as a BootP or DHCP server) or a directed broadcast address. IP helper addresses allow the routing switch to forward requests for certain UDP applications from a client on one subnet to a server on another subnet. None configured Configuring an IP helper address

[*] See the chapter "Configuring IP Addressing" in the Management and Configuration Guide for your switch.