Command Line Interface
4-112
4
Command Mode
Interface Configuration (Ethernet)
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, 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), VLAN identifier, and port
identifier.
• Static addresses entered in the source guard binding table with the ip
source-guard binding command (page 4-113) 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 (page 4-115), 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 or dynamic DHCP snooping binding, the
packet will be forwarded.
- If IP source guard if enabled on an interface for which IP source bindings
(dynamically learned via DHCP snooping or manually configured) are not
yet configured, the switch will drop all IP traffic on that port, except for
DHCP packets.
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