Messages in this thread | | | Date | Fri, 29 Jun 2007 13:39:22 +0200 | From | Patrick McHardy <> | Subject | Re: mss to pmtu clamping partially broken? |
| |
Andreas Steinmetz wrote: > There seems to be a problem with mss to pmtu clamping for incoming syn > packets on reply to an outgoing connection on a ppp interface. The mss > of the outgoing syn packets is always always clamped to the pmtu, I did > check this with a target host I do have access to. The incoming syn > reply to such a packet, however, is mss clamped only sometimes and this > seems to depend on the DSL line used. > > The kernels tested were 2.6.20.1, 2.6.20.3 and 2.6.22rc6. > > Test setup: Two DSL lines, otherwise identical setup (same masquerading > linux gateway, same DSL account, same DSL modem, same DSL line provider, > same target host, request from and tcpdump on the same client). > > Linux Client<->Masquerading Linux Gateway<->DSL Modem<->DSL Line<->... > > DSL line 1, working: > > 22:26:39.319281 IP (tos 0x0, ttl 64, id 22377, offset 0, flags [DF], > length: 48 > ) 192.168.0.253.1164 > 64.34.165.170.80: S [tcp sum ok] > 1465827859:1465827859(0) > win 5840 <mss 1460,nop,nop,sackOK> > 22:26:39.459314 IP (tos 0x0, ttl 51, id 0, offset 0, flags [DF], > length: 48) 64 > .34.165.170.80 > 192.168.0.253.1164: S [tcp sum ok] > 3667852791:3667852791(0) ack > 1465827860 win 5840 <mss 1452,nop,nop,sackOK> > > The tcpdump on the client shows that the mss of the incoming syn reply > packet is clamped to the ppp interface mtu. > > DSL line 2, not working: > > 22:03:57.725998 IP (tos 0x0, ttl 64, id 55984, offset 0, flags [DF], > length: 48 > ) 192.168.0.253.1600 > 64.34.165.170.80: S [tcp sum ok] > 36968258:36968258(0) win > 5840 <mss 1460,nop,nop,sackOK> > 22:03:57.866966 IP (tos 0x0, ttl 51, id 0, offset 0, flags [DF], > length: 48) 64 > .34.165.170.80 > 192.168.0.253.1600: S [tcp sum ok] > 2226854208:2226854208(0) ack > 36968259 win 5840 <mss 1460,nop,nop,sackOK> > > The tcpdump on the client shows that the mss of the incoming syn reply > packet is *NOT* clamped to the ppp interface mtu.
You forgot to mention *how* you're clamping the MSS. Using TCPMSS? Do you have a rule for incoming packets?
- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
| |