Cisco Cisco IOS Software Release 12.2(8)T
SIP Gateway Support for the Bind Command
Feature Overview
3
Cisco IOS Release 12.2(8)T and 12.2(11)T
Feature Overview
In previous releases of Cisco IOS software, the source address of a packet going out of the gateway was
never deterministic. That is, the session protocols and VoIP layers always depended on the IP layer to
give the best local address. The best local address was then used as the source address (the address
showing where the SIP request came from) for signaling and media packets. Using this nondeterministic
address occasionally caused confusion for firewall applications, as a firewall could not be configured
with an exact address and would take action on several different source address packets.
never deterministic. That is, the session protocols and VoIP layers always depended on the IP layer to
give the best local address. The best local address was then used as the source address (the address
showing where the SIP request came from) for signaling and media packets. Using this nondeterministic
address occasionally caused confusion for firewall applications, as a firewall could not be configured
with an exact address and would take action on several different source address packets.
However, the bind interface command allows you to configure the source IP address of signaling and
media packets to a specific interface’s IP address. Thus, the address that goes out on the packet is bound
to the IP address of the interface specified with the bind command. Packets that are not destined to the
bound address are discarded.
media packets to a specific interface’s IP address. Thus, the address that goes out on the packet is bound
to the IP address of the interface specified with the bind command. Packets that are not destined to the
bound address are discarded.
When you do not want to specify a bind address, or if the interface is down, the IP layer still provides
the best local address.
the best local address.
The bind command performs different functions based on the state of the interface:
Interface State
Result Using Bind Command
Shutdown
With or without active calls
The Transmission Control Protocol (TCP) and User Datagram Protocol (UDP)
socket listeners are initially closed. (Socket listeners receive datagrams addressed
to the socket.)
socket listeners are initially closed. (Socket listeners receive datagrams addressed
to the socket.)
Then the sockets are opened to listen to any IP address.
If the outgoing gateway has the bind command enabled and has an active call, the
call becomes a one-way call with media flowing from the outgoing gateway to the
terminating gateway.
call becomes a one-way call with media flowing from the outgoing gateway to the
terminating gateway.
No Shutdown
No Active Calls
The TCP and UDP socket listeners are initially closed. (Socket listeners receive
datagrams addressed to the socket.)
datagrams addressed to the socket.)
Then the sockets are opened and bound to the IP address set by the bind command.
The sockets accept packets destined for the bound address only.
No Shutdown
Active Calls
The TCP and UDP socket listeners are initially closed.
Then the sockets are opened to listen to any IP address.
Bound interface’s IP address is
removed
removed
The TCP and UDP socket listeners are initially closed.
Then the sockets are opened to listen to any address, because the IP address has
been removed.
been removed.
A message stating that the IP address has been deleted from SIP bound interface is
printed.
printed.
If the outgoing gateway has bind enabled and has an active call, the call becomes
a one-way call with media flowing from the outgoing gateway to the terminating
gateway.
a one-way call with media flowing from the outgoing gateway to the terminating
gateway.