Lucent Technologies P550 - Manual (Page 27)

Cajun P550 Switch Overview
Cajun P550/P220 Switch Operation Guide 1-7
Cajun Routing Overview
The Cajun switch is an IP and IPX router with virtual interfaces. Virtual interfaces are
mapped to physical ports or VLANs. Layer 3 IP traffic is routed between the virtual
interfaces.
Ports become members of VLANs by assignment or by rules. Multiple VLANs can share a
single trunk port. In contrast, multiple physical ports can be associated with a single
VLAN. In all cases, traffic that arrives and leaves the same VLAN is bridged, not routed.
This section provides additional information that includes:
❒ Compatibility with the Layer 2 Switch
❒ Routing with Layer 2 and Layer 3 Modules
Compatibility with the Layer 2 Switch
The switch is completely backwards compatible with all of the Layer 2 media modules
currently supported in the Cajun switch. Traffic from the Layer 2 media module is routed
by sending that traffic to the routing engine on the Layer 3 supervisor module. The
supervisor module routes all traffic from Layer 2 media modules in software as described
in the section, “Routing with Layer 2 and Layer 3 Modules”.
Note: Layer 2 traffic that does not require routing is bridged independently of the
Layer 3 traffic based on the MAC address or VLAN information.
Routing with Layer 2 and Layer 3 Modules
When the Cajun switch is configured with a mix of Layer 2 and Layer 3 modules, IP and
IPX routing is performed by the Layer 3 media module or the Layer 3 supervisor module
using special ASICs present on those modules. These ASICs contain an address cache
(forwarding table) that can hold a maximum of 20,000 address cache entries. The entries
consist of packet addressing information and next hop information that enable the
switch to effectively route the packets to their destination.
The Layer 3 supervisor also maintains a master routing table. The master routing table
contains up to 24,000 entries. This routing table enables the supervisor module to keep
track of which entries are in each address cache. As a result, each time a change occurs
in the master routing table, the Layer 3 supervisor module updates the appropriate
address caches. For example, if a unicast route is removed from the master routing table,
then all matching entries in forwarding tables are removed as well.