Brocade Communications Systems ICX 7250 series, Руководство по настройке

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IP forwarding cache
The IP forwarding cache provides a fast-path mechanism for forwarding IP packets. The cache contains entries for IP destinations. When
a Brocade Layer 3 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 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 final destination. The port numbers are
the ports through which the destination can be reached.
• If the cache does not contain an entry and the traffic does not qualify for an entry in the session table instead, the software can
create an entry in the forwarding cache.
Each entry in the IP forwarding cache has an age timer. If the entry remains unused for ten minutes, the software removes the entry. The
age timer is not configurable.
Here is an example of an entry in the IP forwarding cache.
IP Address Next Hop MAC Type Port Vlan Pri
1 192.168.1.11 DIRECT 0000.0000.0000 PU n/a 0
Each IP forwarding cache entry contains the IP address of the destination, and the IP address and MAC address of the next-hop router
interface to the destination. If the destination is actually an interface configured on the Layer 3 switch 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 4 QoS priority
associated with the destination if applicable.
NOTE
You cannot add static entries to the IP forwarding cache, although you can increase the number of entries the cache can
contain. Refer to the section "Displaying and modifying system parameter default settings" in the
Brocade FastIron Layer 2
Switching Configuration Guide .
Layer 4 session table
The Layer 4 session provides a fast path for forwarding packets. A session is an entry that contains complete Layer 3 and Layer 4
information for a flow of traffic. Layer 3 information includes the source and destination IP addresses. Layer 4 information includes the
source and destination TCP and UDP ports. For comparison, the IP forwarding cache contains the Layer 3 destination address but does
not contain the other source and destination address information of a Layer 4 session table entry.
The Layer 2 switch or Layer 3 switch selects the session table instead of the IP forwarding table for fast-path forwarding for the following
features:
• Layer 4 Quality-of-Service (QoS) policies
• IP access policies
To increase the size of the session table, refer to the section "Displaying and modifying system parameter default settings" in the
Brocade FastIron Layer 2 Switching Configuration Guide . The ip-qos-session parameter controls the size of the session table.
IP route exchange protocols
Brocade Layer 3 switches support the following IP route exchange protocols:
• Routing Information Protocol (RIP)
• Open Shortest Path First (OSPF)
• Border Gateway Protocol version 4 (BGP4)
IP configuration overview
Brocade FastIron Layer 3 Routing Configuration Guide
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