The NZ Linux Resource

[wailug] w2000 vpn

Tony Arcus Tony at access-info.co.nz
Tue Jul 15 08:31:05 NZST 2003


Thanks Nic,
here is a tcpdump of a session

tcpdump -pnvi ppp0 host 202.89.41.34 and not port 23
tcpdump: listening on ppp0
08:23:13.329836 202.27.208.8.61399 > 202.89.41.34.1723: S [tcp sum ok] 
2421251911:2421251911(0) win 64240 <mss 1460,nop,nop,sackOK> (DF) (ttl 127, id 
4611, len 48)
08:23:13.509801 202.89.41.34.1723 > 202.27.208.8.61399: S [tcp sum ok] 
1391229001:1391229001(0) ack 2421251912 win 5840 <mss 1460,nop,nop,sackOK> (DF) 
[tos 0x80]  (ttl 56, id 0, len 48)
08:23:13.510392 202.27.208.8.61399 > 202.89.41.34.1723: . [tcp sum ok] ack 1 
win 64240 (DF) (ttl 127, id 4613, len 40)
08:23:13.510576 202.27.208.8.61399 > 202.89.41.34.1723: P 1:157(156) ack 1 win 
64240 (DF) (ttl 127, id 4614, len 196)
08:23:13.719793 202.89.41.34.1723 > 202.27.208.8.61399: . [tcp sum ok] ack 157 
win 6432 (DF) [tos 0x80]  (ttl 56, id 6473, len 40)
08:23:13.739784 202.89.41.34.1723 > 202.27.208.8.61399: P 1:157(156) ack 157 
win 6432 (DF) [tos 0x80]  (ttl 56, id 6474, len 196)
08:23:13.740941 202.27.208.8.61399 > 202.89.41.34.1723: P 157:325(168) ack 157 
win 64084 (DF) (ttl 127, id 4616, len 208)
08:23:13.939761 202.89.41.34.1723 > 202.27.208.8.61399: P [tcp sum ok] 157:189
(32) ack 325 win 7504 (DF) [tos 0x80]  (ttl 56, id 6475, len 72)
08:23:13.939802 202.89.41.34 > 202.27.208.8: gre 202.89.41.34 > 202.27.208.8: 
[KS] gre-proto-0x880B (DF) [tos 0x80]  (ttl 56, id 24858, len 65)
08:23:13.940001 202.27.208.8 > 202.89.41.34: icmp: 202.27.208.8 protocol 47 
unreachable [tos 0xc0]  (ttl 255, id 57926, len 93)
08:23:13.942586 202.27.208.8.61399 > 202.89.41.34.1723: P [tcp sum ok] 325:349
(24) ack 189 win 64052 (DF) (ttl 127, id 4618, len 64)
08:23:14.119785 202.89.41.34.1723 > 202.27.208.8.61399: F [tcp sum ok] 189:189
(0) ack 325 win 7504 (DF) [tos 0x80]  (ttl 56, id 6476, len 40)
08:23:14.120570 202.27.208.8.61399 > 202.89.41.34.1723: F [tcp sum ok] 349:349
(0) ack 190 win 64052 (DF) (ttl 127, id 4621, len 40)
08:23:14.139798 202.89.41.34.1723 > 202.27.208.8.61399: R [tcp sum ok] 
1391229190:1391229190(0) win 0 (DF) [tos 0x84]  (ttl 247, id 0, len 40)
08:23:14.289767 202.89.41.34.1723 > 202.27.208.8.61399: R [tcp sum ok] 
1391229191:1391229191(0) win 0 (DF) [tos 0x84]  (ttl 247, id 0, len 40)

AND
tcpdump -pnvi eth0 host 202.89.41.34 and not port 23
tcpdump: listening on eth0
08:23:50.760625 192.168.20.19.1327 > 202.89.41.34.1723: S [tcp sum ok] 
2429914894:2429914894(0) win 64240 <mss 1460,nop,nop,sackOK> (DF) (ttl 128, id 
4696, len 48)
08:23:50.919851 202.89.41.34.1723 > 192.168.20.19.1327: S [tcp sum ok] 
1421680695:1421680695(0) ack 2429914895 win 5840 <mss 1460,nop,nop,sackOK> (DF) 
[tos 0x80]  (ttl 55, id 0, len 48)
08:23:50.920426 192.168.20.19.1327 > 202.89.41.34.1723: . [tcp sum ok] ack 1 
win 64240 (DF) (ttl 128, id 4698, len 40)
08:23:50.920641 192.168.20.19.1327 > 202.89.41.34.1723: P 1:157(156) ack 1 win 
64240 (DF) (ttl 128, id 4699, len 196)
08:23:51.119877 202.89.41.34.1723 > 192.168.20.19.1327: . [tcp sum ok] ack 157 
win 6432 (DF) [tos 0x80]  (ttl 55, id 20391, len 40)
08:23:51.139836 202.89.41.34.1723 > 192.168.20.19.1327: P 1:157(156) ack 157 
win 6432 (DF) [tos 0x80]  (ttl 55, id 20392, len 196)
08:23:51.140814 192.168.20.19.1327 > 202.89.41.34.1723: P 157:325(168) ack 157 
win 64084 (DF) (ttl 128, id 4701, len 208)
08:23:51.349861 202.89.41.34.1723 > 192.168.20.19.1327: P [tcp sum ok] 157:189
(32) ack 325 win 7504 (DF) [tos 0x80]  (ttl 55, id 20393, len 72)
08:23:51.352535 192.168.20.19.1327 > 202.89.41.34.1723: P [tcp sum ok] 325:349
(24) ack 189 win 64052 (DF) (ttl 128, id 4703, len 64)
08:23:51.354956 192.168.20.19 > 202.89.41.34: gre 192.168.20.19 > 202.89.41.34: 
[KS] gre-proto-0x880B (ttl 128, id 4704, len 80)
08:23:51.529848 202.89.41.34.1723 > 192.168.20.19.1327: F [tcp sum ok] 189:189
(0) ack 325 win 7504 (DF) [tos 0x80]  (ttl 55, id 20394, len 40)
08:23:51.530207 192.168.20.19.1327 > 202.89.41.34.1723: F [tcp sum ok] 349:349
(0) ack 190 win 64052 (DF) (ttl 128, id 4705, len 40)
08:23:51.549845 202.89.41.34.1723 > 192.168.20.19.1327: R [tcp sum ok] 
1421680884:1421680884(0) win 0 (DF) [tos 0x84]  (ttl 246, id 0, len 40)
08:23:51.689838 202.89.41.34.1723 > 192.168.20.19.1327: R [tcp sum ok] 
1421680885:1421680885(0) win 0 (DF) [tos 0x84]  (ttl 246, id 0, len 40)

Any help appreciated.
-- 
Access Information Limited
Waitangi Rd f4
PO Box 122
Carterton
Wairarapa
06-379-6668 * 021-827-660
tony at access-info.co.nz
www.access-info.co.nz


Quoting Nic Bellamy <nic at bellamy.co.nz>:

> On Mon, 2003-07-14 at 17:53, Tony Arcus wrote:
> > Question:
> > What is needed to set up pptp with the following configuration:
> > 
> > 
> > ME with } 
> > Win2000 }-----RH6.2------internet-----a firewall----customers network
> >              ipchains
> 
> >From memory (as in: it's been a while since I've done anything serious
> with it), ipchains doesn't handle address translation of protocols other
> than TCP/UDP/ICMP very well. Although it *should* be able to handle a
> single outgoing PPTP connection ok (running multiple tunnels, or running
> a PPTP server behind NAT, is where you start needing special support).
> 
> What's happening on your firewall - is it blocking either the outgoing
> or returning GRE packets (IP protocol 47)?
> 
> Cheers,
> 	Nic.
> 
> -- 
> Nic Bellamy <nic at bellamy.co.nz>
> Bellamy Consulting (NZ) Limited. +64-6-377-4957 Mobile: +64-21-251-8954
> Internet Software & Security Consulting -- http://www.bellamy.co.nz/ --
> 
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> 


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