IP Networking: no 2-way audio using IP trunk

[Sobomax]

Hi,
We have a problem with IP trunk between 2 3300 - CXII and MXe III.
There is dead silent when you call from one site to another using IP trunk.
What's the problem??

[Mitel100]

This is normally down to a gateway issue, the phones may not be getting the correct gateway information.

It would be good to check what gateway the phones have received via DHCP. When you log into the controller ESM, filter down to 'All IP Telephones' form and check the gateway the phones have and ensure it has the correct one.

[martyn]

First place I would start looking is that there is routing between the two voice networks. If it can only go one way and not the other, then you will end up with one way voice.

[Sobomax]

More detailed information:
Have 2 sites - Site A and Site BBetween the sites there is a VPN running on routers under FreeBSD.
Any traffic between the sites is allowed.
IP settings for Site A: 192.168.0.0/24
3300: 192.168.0.2
g/w: 192.168.0.1
DHCP scope: 192.168.0.20-192.168.0.254IP

settings for Site B: 192.168.2.0/24
3300: 192.168.2.2
g/w: 192.168.2.1
DHCP scope: 192.168.2.20-192.168.2.254

What we found is that we need to assign lower MTU on the controller, becouse there are some restrictions about this:
VC1iskra ~]# ping -s 1472 192.168.0.2
PING 192.168.0.2 (192.168.0.2): 1472 data bytes1480 bytes from 192.168.0.2: icmp_seq=0 ttl=63 time=9.438 ms
1480 bytes from 192.168.0.2: icmp_seq=1 ttl=63 time=9.304 ms
^C
--- 192.168.0.2 ping statistics ---2 packets transmitted, 2 packets received, 0.0% packet loss
round-trip min/avg/max/stddev = 9.304/9.371/9.438/0.067 ms
VC1iskra ~]# ping -s 1473 192.168.0.2
PING 192.168.0.2 (192.168.0.2): 1473 data bytes
^C
--- 192.168.0.2 ping statistics ---2 packets transmitted, 0 packets received, 100.0% packet loss

How can I do this. I only khow about DHCP option 26. Are there any other ways to change MTU on the controller? 

 
I've also checked the IP setting on phones via IP Telephones-All form and they are correct.
 

[stevek]

You lose the additional bytes due to the encryption overhead. This was also common fault on early ADSL implementations.

If the packet being generated has the DF bit set it (router?) will drop the packet.

You would need to set the mtu size on the interface the tunnel terminates on not the end devices then the terminating interfaces know to fragment and strip the DF bit.
On cisco would be
Router(config)#interface x/y
Router(config-if)#ip mtu 1472

Changing the MTU size permanently under FreeBSD

Set MTU settings by editing /etc/rc.conf file:

vi /etc/rc.conf
Modify interface xl0 as follows, enter:

1 ifconfig_xl0="inet x.x.x.x netmask y.y.y.y mtu 1472"
Save and close the file.

Restart the network:
/etc/rc.d/netif restart