PMTU is not working for IPv6-ESP

PMTU is not working for IPv6-ESP

[Bhat, Jayalakshmi Manjunath]

Hi All,

We are executing a ping test in TUNNEL mode. This is to test PMTU. The test configurations are as below.

IP address of our device: 	3000::268:ebff:fe85:539f	
IP address of Host1	:	3002::200:10ff:fe10:1280
SGW (Gateway address):	3001::200:10ff:fe10:1161

1. SGW sends ICMPv6 Echo Request from Host1 to our device within ESP 
2. Our device responds back with ICMPv6 Echo Reply to Host1 within ESP Tunnel

3. SGW sends ICMPv6 Echo Request fragments totalling 1500 Bytes from Host1 to our device within ESP Tunnel 
4. Our device reassembles ICMPv6 Echo Request and transmits fully assembled ICMPv6 Echo Reply to Host1 within ESP Tunnel

5. SGW sends ICMPv6 Packet Too Big Message within ESP Tunnel to our device 
6. SGW sends ICMPv6 Echo Request fragments totalling 1500 Bytes from Host1 to our device within ESP Tunnel 
7. Our device reassembles ICMPv6 Echo Request and transmits fragmented ICMPv6 Echo Reply to Host1 within ESP Tunnel 

Now device fails at step7. When I looked into esp6.c, I found that ip6_path_mtu setting never gets invoked. This is done in esp6_err function.
I am not seeing this function being invoked at all. 

I am not sure when this function is supposed to get called.

It would help a lot if any one can give me inputs.

Regards,
Jayalakshmi