GLBP on interface used for SIP signaling

[Michael Marzol]

We have a 3945 router being used as a VXML gateway as well as for CUBE. Our signaling address for SIP back to Paetec is 10.15.50.5. We aquired a new 3945 and thought we could use it for load balancing in conjunction with our current 3945 by using GLBP. After configuring them and making a few inbound test calls, I find that the signaling address has now become the new physical address of the interfaces as opposed to the virtual IP of 10.15.50.5. Of course the calls fail. I understand that the 'bind media/control source-interface' command will use the physical address of the interface. My question is, is there any way around this in order for the media/signaling binding to remain on the virtual IP of 10.15.50.5? Configuration below.

AVF Router:

interface GigabitEthernet0/0
ip address 10.15.50.3 255.255.255.0
glbp 100 timers 5 18
glbp 100 priority 150
glbp 100 authentication text SSCGLBP
glbp 100 preempt
glbp 100 load-balancing round-robin
glbp 100 ip 10.15.50.5

AVG Router:

interface GigabitEthernet0/0
ip address 10.15.50.4 255.255.255.0
glbp 100 timers 5 18
glbp 100 priority 100
glbp 100 authentication text SSCGLBP
glbp 100 preempt
glbp 100 load-balancing round-robin
glbp 100 ip 10.15.50.5

voice service voip

allow-connections sip to sip

no supplementary-service sip moved-temporarily

no fax-relay sg3-to-g3

modem passthrough nse codec g711ulaw

sip

bind control source-interface GigabitEthernet0/0

  bind media source-interface GigabitEthernet0/0

  header-passing error-passthru

  early-offer forced

  midcall-signaling passthru

  sip-profiles 100 voice service voip
allow-connections sip to sip
no supplementary-service sip moved-temporarily
no fax-relay sg3-to-g3
modem passthrough nse codec g711ulaw
sip
  bind control source-interface GigabitEthernet0/0
  bind media source-interface GigabitEthernet0/0
  header-passing error-passthru
  early-offer forced
  midcall-signaling passthru
  sip-profiles 100

[Gautam Renjen]

Hi Strangeroad,

1. GLBP for load-balancing is not going to work in your scenario if my understand of the topology is as below:

           |---------3945 AVF----Gig0/0---------|

Inside---|                                             |--------Paetec

            |--------3945 AVG---Gig0/0---------|

If this is so, GLBP mac will be learnt during ARP and cached for a few hours, and all traffic will hit one router and not the other.

2. As bind is only for inteface and providing an ip is not an option, you might look into using loopback intefaces to terminate the SIP sessions and bind to that interface.

3. To keep that virtual IP, you can configure ip nat inside on the loopback and ip nat outside on the gig, and nat that particular IP flow by using a nat acl .

My 2 cents as a non VoIP engineer, and I could be totally off here, so please confirm with someone else or TAC.