Installation and Getting Started Guide

address and TCP or UDP port listed in the session table entry and sending the packet to a queue on the outgoing port(s) listed in the session table. The routing switch selects the queue based on the Quality of Service (QoS) level associated with the session table entry.

3.If the session table does not contain an entry that matches the packet’s source address and TCP or UDP port, the routing switch looks in the IP forwarding cache for an entry that matches the packet’s destination IP address. If the forwarding cache contains a matching entry, the routing switch forwards the packet to the IP address in the entry. The routing switch sends the packet to a queue on the outgoing port(s) listed in the forwarding cache. The routing switch selects the queue based on the Quality of Service (QoS) level associated with the forwarding cache entry.

4.If the IP forwarding cache does not have an entry for the packet, the routing switch checks the IP route table for a route to the packet’s destination. If the IP route table has a route, the routing switch makes an entry in the session table or the forwarding cache, and sends the route to a queue on the outgoing port(s).

•If the running-config contains a Policy-Based Routing (PBR) definition or an IP access policy for the packet, the software makes an entry in the session table. The routing switch uses the new session table entry to forward subsequent packets from the same source to the same destination.

•If the running-config does not contain a PBR definition or an IP access policy for the packet, the software creates a new entry in the forwarding cache. The routing switch uses the new cache entry to forward subsequent packets to the same destination.

The following sections describe the IP tables and caches:

•ARP cache and static ARP table

•IP route table

•IP forwarding cache

•IP session table

The software enables you to display these tables. You also can change the capacity of the tables on an individual basis if needed by changing the memory allocation for the table.

ARP Cache and Static ARP 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 IP 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 can contain dynamic (learned) entries and static (user-configured) 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:

 

IP Address

MAC Address

Type

Age

Port

1

207.95.6.102

0800.5afc.ea21

Dynamic

0

6

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

Static ARP Table

In addition to the ARP cache, routing switches have a static ARP table. Entries in the static ARP table are user­ configured. You can add entries to the static ARP table regardless of whether the device the entry is for is connected to the routing switch.

NOTE: The routing switches have a static ARP table but the HP 6208M-SX does not.

The software places an entry from the static ARP table into the ARP cache when the entry’s interface comes up.

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