On 25/08/2014 12:36, Mikael Abrahamsson wrote:
So which one is correct? I have talked to numerous people and they have different experience and results are contradicting.
looks like you're correct. Given the following test configuration:
interface GigabitEthernet0/0/0/10 mtu 9200 ipv4 address 10.232.1.1/24 interface GigabitEthernet0/0/0/10.100 ipv4 address 10.232.100.1/24 encapsulation dot1q 100 interface GigabitEthernet0/0/0/10.200 ipv4 address 10.232.200.1/24 encapsulation dot1q 200 second-dot1q 201
The mtu config for each of these is (in order): gi0/0/0/10:
Protocol Caps (state, mtu) -------- ----------------- None ether (down, 9200) arp arp (down, 9186) ipv4 ipv4 (down, 9186) ether_sock ether_sock (down, 9186) vlan vlan_target (down, 9186)
gi0/0/0/10.100:
None vlan_jump (down, 9204) None dot1q (down, 9204) arp arp (down, 9186) ipv4 ipv4 (down, 9186)
gi0/0/0/10.200:
None vlan_jump (down, 9208) None dot1q (down, 9208) arp arp (down, 9186) ipv4 ipv4 (down, 9186)
i.e. the ipv4 / ipv6 / arp MTU in each case is 9200 - 14 = 9186. In order to compensate for the single vlan tagging on the .100 interface and the double tagging on the .200 interface, the vlan MTU is increased to 9204 and then to 9208 bytes respectively. There is no need to adjust for the vlan tags.
Nick _______________________________________________ cisco-nsp mailing list [email protected] https://puck.nether.net/mailman/listinfo/cisco-nsp archive at http://puck.nether.net/pipermail/cisco-nsp/
