6-to-4 Tunneling

[Sherry1]

Hi, Guys.

May I know is there any schemes that we can use to overcome the datagram fragmentation problem in the IPv4 tunnel for 6-to-4 tunneling ?

Thanks

[Hector Gustavo Serrano Gutierrez]

The default MTU is 1500.

When using any kind of overlay technique (which requires "encapsulation") there is the possibility traffic can be fragmented since the packet can go beyond the 1500 MTU size.

When using the interface Tunnel command on Cisco Routers in order to configure one type of tunneling technique, you can attempt to avoid fragmentation by adding to the Tunnel configuration the next commands:

interface TunnelX
 ip mtu 1400
 ip tcp adjust-mss 1360

Regards.

PS: An informative article is Resolve IPv4 Fragmentation, MTU, MSS, and PMTUD Issues with GRE and IPsec