no ip proxy-arp command impact voice traffic?

Answered Question
May 2nd, 2010

Hi All,

no ip proxy-arp will impact any voice traficc incomming and outgoing calls.

scenario

------------

Vlan500(Voice-vlan)------------voice-gateway----------pstn

when i disabled the proxy-arp in the vlan500svi,the outging and incomming calls disrupted.

internal calls are working fine.

I have this problem too.
0 votes
Correct Answer by Giuseppe Larosa about 3 years 11 months ago

Hello Subashmbi,

we have seen that the VGW is connected to another IP subnet in Vlan 221.

In vlan 500, where you have disabled the ip proxy-arp there can be IP phones and/or the Call Manager/ IP PBX

For Cisco CallManager:

Signalling is between Call Manager and IP phones (SCCP or SIP) and between Call Manager and voice gateway (either using H.323 or MGCP).

RTP VoIP streams for the VoIP call leg is between the Voice Gateway and the involved IP phone.

No direct signalling traffic flows between the IP phone and the VGW.

Or signaling had been broken or the RTP stream had been broken, when you disabled the IP proxy ARP in Vlan 500 SVI.

Hope to help

Giuseppe

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Giuseppe Larosa Sun, 05/02/2010 - 11:57

Hello Subashmbi,

if the voice gateway was relying on proxy ARP on SVI vlan 500 of connected multilayer switch the effects can be similar to what you describe.

All the difference is made of how a static route is defined:

ip route 10.0.0.0 255.0.0.0 fas0/0   on VGW  >>>  VGW relies on proxy ARP

ip route 10.0.0.0 255.0.0.0    >>>>> VGW  knows an IP next-hop in subnet and does not rely on Proxy ARP enabled on multilayer switch

So check how the VGW is configured and you can fix it as described above (if it using static routes )

Hope to help

Giuseppe

subashmbi Sun, 05/02/2010 - 12:05

Hi Gilsar,

Thanks for the update.

ip route 172.16.81.200 255.255.255.255 10.88.221.200-----Point to the VGW loopback interface signalling in the core-switch.

Voice-gtw routing

----------------------------

ip route 0.0.0.0 0.0.0.0 172.16.81.254
ip route 172.16.81.0 255.255.255.0 10.88.221.254

for more reference i am attaching the configs

Attachment: 
Giuseppe Larosa Sun, 05/02/2010 - 12:12

Hello Subashmbi,

>> ip route 0.0.0.0 0.0.0.0 172.16.81.254
ip route 172.16.81.0  255.255.255.0 10.88.221.254

if the connected subnet in Vlan 500  is 10.88.221.0/24 use :

no ip route 0.0.0.0 0.0.0.0 172.16.81.254

ip route 0.0.0.0 0.0.0.0 10.88.221.254

You were using recursion for the next-hop of default static route, if VGW sends out an ARP request for 172.16.81.254 on 10.88.221.0/24 IP subnet with proxy ARP disabled it cannot solve it.

I agree it should sends out an ARP request for 10.88.221.254 only as for the second static route that specifies that subnet 172.16.81.0/24 is reachable via 10.88.221.254.

Edit:

After examing your attachments

if the VGW is connected to port G0/1 in vlan 221 and you change the proxy-ARP settings in vlan 500, then all the effects are on devices on vlan500.

Do the phones have a default gateway set = vlan 500 SVI ip address, if not the proxy-ARP allows them to send traffic to the VGW

Hope to help

Giuseppe

subashmbi Sun, 05/02/2010 - 12:34

These configuration are simulated in the lab. I faced this issue today. when i disabled the proxy-arp my incoming & outgoing calls disconnected. after i enabled, it,s working fine....

After examing your attachments

if the VGW is connected to port  G0/1 in vlan 221 and you change the proxy-ARP settings in vlan 500,  then all the effects are on devices on vlan500.

Yes.

Do the phones have a default  gateway set = vlan 500 SVI ip address, if not the proxy-ARP allows them  to send traffic to the VGW

Yes, Phone ip address is getting from dhcp.

Giuseppe Larosa Sun, 05/02/2010 - 14:18

Hello Subashmbi,

>>

Do the phones have a default  gateway set = vlan 500 SVI ip address,  if not the proxy-ARP allows them  to send traffic to the VGW

Yes, Phone  ip address is getting from dhcp.

What about the CallManager or other IP PBX you are using?

It also needs to be able to reach VGW loopback ip address, if it is in vlan500 it might be the one that was relying on proxy ARP.

Hope to help

Giuseppe

subashmbi Sun, 05/02/2010 - 20:48

Hi Guilsar,

I checked from the VGW side to reach call manager.

In Call manager some entry is there to point this loopback address(signalling interface) thats what my calls are going outside?.I didn,t checked the reachability.

Correct Answer
Giuseppe Larosa Mon, 05/03/2010 - 10:31

Hello Subashmbi,

we have seen that the VGW is connected to another IP subnet in Vlan 221.

In vlan 500, where you have disabled the ip proxy-arp there can be IP phones and/or the Call Manager/ IP PBX

For Cisco CallManager:

Signalling is between Call Manager and IP phones (SCCP or SIP) and between Call Manager and voice gateway (either using H.323 or MGCP).

RTP VoIP streams for the VoIP call leg is between the Voice Gateway and the involved IP phone.

No direct signalling traffic flows between the IP phone and the VGW.

Or signaling had been broken or the RTP stream had been broken, when you disabled the IP proxy ARP in Vlan 500 SVI.

Hope to help

Giuseppe

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