Chapter 63 System
ZyWALL Series CLI Reference Guide
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63.12 Fast Forwarding
Fast Forwarding maximizes the network performance of the Zyxel Device, by enabling a faster packet
switching method which uses a trie (prefix tree).
When Fast Forwarding is enabled, essential network services such as NAT, routing, firewall, and VPN work
as expected. However, security and logging services such as UTM, web authentication, MAC address
binding, BWM, and traffic statistics are bypassed. This means traffic passes through theZyxel Device
unchecked and unlogged.
Note: Enabling fast forward might expose your network to security threats. We recommend enabling fast
forwarding temporarily and only when it is needed
63.12.1 Fast Forwarding Technical Overview
When switching a packet, a network device examines the packet’s destination and then searches its
local route cache to determine the output interface and the next hop to the destination. The route
cache must be periodically cleared of old and invalid entries, to prevent the cache from consuming
too much memory.
Fast Forwarding improves route cache performance by using a trie (prefix tree). A trie is a 256-way
binary tree that does not store any data. Instead, each leaf in the tree contains a pointer to data in a
separate adjacency table. The routing cache stores destination information in the search tree, and
information about how to reach each destination in the adjacency table. Separating the routing cache
into two data structures offers several advantages:
• The search tree and adjacency table can be created and recreated separately.
• Modifying entries in the adjacency table does not invalidate entries in the search tree.
• Entries in the adjacency table can point to each other, speeding up recursive routing. Recursive
routing is where a device looks up a packet’s next hop in the routing cache but does not know how
to reach the next hop, requiring another lookup.
• The adjacency table can be updated directly from the device’s ARP cache and routing table. This
eliminates the need to periodically clear old and invalid entries from the cache.
63.12.2 Fast Forwarding Commands
The following table describes the commands available for fast forwarding. You must use the
configure terminal command to enter the configuration mode before you can use these
commands.
Table 304 Command Summary: Fast Forwarding
COMMAND DESCRIPTION
fast forwarding {activate |
deactivate}
Enables or disables fast forwarding on the Zyxel Device.
show fast forwarding status
Displays whether fast forwarding is currently enabled.
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