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22-6
Command Usage
• Source guard is used to filter traffic on an unsecure port which receives
messages from outside the network or firewall, and therefore may be
subject to traffic attacks caused by a host trying to use the IP address
of a neighbor.
• Setting source guard mode to “sip” or “sip-mac” enables this function
on the selected port. Use the “sip” option to check the VLAN ID,
source IP address, and port number against all entries in the binding
table. Use the “sip-mac” option to check these same parameters, plus
the source MAC address. Use the no source guard command to
disable this function on the selected port.
• When enabled, traffic is filtered based upon dynamic entries learned
via DHCP snooping, static entries configured in the DHCP snooping
table, or static addresses configured in the source guard binding table.
• Table entries include a MAC address, IP address, lease time, entry type
(Static-IP-SG-Binding, Dynamic-DHCP-Binding,
Static-DHCP-Binding), VLAN identifier, and port identifier.
• Static addresses entered in the source guard binding table with the ip
source-guard binding command (page 22-7) are automatically
configured with an infinite lease time. Dynamic entries learned via
DHCP snooping are configured by the DHCP server itself; static
entries include a manually configured lease time.
• If the IP source guard is enabled, an inbound packet’s IP address (sip
option) or both its IP address and corresponding MAC address
(sip-mac option) will be checked against the binding table. If no
matching entry is found, the packet will be dropped.
• Filtering rules are implemented as follows:
- If the DHCP snooping is disabled (see page 22-11), IP source guard
will check the VLAN ID, source IP address, port number, and
source MAC address (for the sip-mac option). If a matching entry is
found in the binding table and the entry type is static IP source guard
binding, the packet will be forwarded.
- If the DHCP snooping is enabled, IP source guard will check the
VLAN ID, source IP address, port number, and source MAC
address (for the sip-mac option). If a matching entry is found in the
binding table and the entry type is static IP source guard binding,