BigIron RX Series Configuration Guide 14953-1001810-01Basic IP parameters and defaults 7IP forwarding cacheThe device maintains a software cache table for fast processing of IP packets that are forwarded orgenerated by the CPU. The cache also contains forwarding information that is normally contained inthe IP routing table. For example, the cache contains information on the physical outgoing port,priority, VLAN, and the type of cache entry. Also, cache entries have hardware information, which isuseful for debugging and aging.There are two types of IP cache entries.1. Directly connected host entries – These entries are created when the CPU receives the firstpacket destined to a directly connected host. Host entries are set to age out after a certainperiod if no traffic is seen for that entry.2. Network entries – These entries are created when a route table entry is created in software.These entries are not subjected to aging. A route table entry is created when routes arelearned by routing protocols such as OSPF or when routes are statically configured.Here is an example of an entry in the IP forwarding cache.Each IP forwarding cache entry contains the IP address of the destination, and the IP address andMAC address of the next-hop router interface to the destination. If the destination is actually aninterface configured on the device itself, as shown here, then next-hop information indicates this.The port through which the destination is reached is also listed, as well as the VLAN and Layer 4QoS priority associated with the destination if applicable.To display the IP forwarding cache, refer to “Displaying the forwarding cache” on page 219.Basic IP parameters and defaultsIP is enabled by default. The following protocols are disabled by default:• Route exchange protocols (RIP, OSPF, BGP4)• Multicast protocols (IGMP, PIM-DM, PIM-SM, DVMRP)• Router redundancy protocols (VRRPE, VRRP, FSRP)When parameter changes take effectMost IP parameters described in this chapter are dynamic. They take effect immediately, as soonas you enter the CLI command. You can verify that a dynamic change has taken effect bydisplaying the running configuration. To display the running configuration, enter the showrunning-config or write terminal command at any CLI prompt.To save a configuration change permanently so that the change remains in effect following asystem reset or software reload, save the change to the startup configuration file. Enter the writememory command from the Privileged EXEC level of any configuration level of the CLI.Changes to memory allocation require you to reload the software after you save the changes to thestartup configuration file. When reloading the software is required to complete a configurationchange, the procedure that describes the configuration change includes a step for reloading thesoftware.IP Address Next Hop MAC Type Port Vlan Pri1 192.168.1.11 DIRECT 0000.0000.0000 PU n/a 0
