Hi, is there any reason why the MTU of a tunnel is hardwired to 1280? For client, it's hardwired in the aiccu client. But after I increase the MTU by hand after setup, I found that the server side is also limited to 1280: 15:51:33.429269 2001:6f8:900:*** > 2001:6f8:900:***: icmp6: too big 1280 I see no reason for a hardwired limit. 1460 for server side should be ok, at least modern Linux kernels have already an automagical MTU detection and usually 1452 are used after tunnel setup on a PPP connection. The reason I'm asking is that I checked the maximum ping6 payload (-s <size>) and found for a 1280 MTU tunnel: 1232: native IPv6 (1280 - 40 - 8) 1190: ESP transport mode AES_128-HMAC_SHA1 1150: ESP tunnel mode AES_128-HMAC_SHA1 (1190 - 40) Peter