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Re: routing problem?
- To: Dani Arbel <darbel(at-nospam)techunix.technion.ac.il>
- Subject: Re: routing problem?
- From: Cedar Cox <cedarc(at-nospam)visionforisrael.com>
- Date: Tue, 4 Sep 2001 17:52:52 +0300 (IDT)
- cc: linux-il(at-nospam)linux.org.il
- Delivered-To: linux.org.il-linux-il@linux.org.il
- In-Reply-To: <Pine.GSO.4.33.0109041032240.9077-100000@techunix.technion.ac.il>
- Sender: linux-il-bounce(at-nospam)cs.huji.ac.il
About the routing table, that's what I thought, although I'm not sure how
they could be simplified. If I understand correctly, 10.0.1.2 should have
nothing to do with 10.0.0.0, but not the other way around. Someone
correct me if I'm wrong, but route's Genmask doesn't really have anything
to do with the interface's netmask, does it? For example, B has is
connected to two ethernets (192.168.1.0 and 192.168.10.0) and C to only
one (192.168.2.0). Is it correct to put a route on C like :
Destination Gateway Genmask Flags Metric Ref Iface
192.168.0.0 10.0.1.1 255.255.240.0 UG 0 0 cipcb0
or should it be
192.168.1.0 10.0.1.1 255.255.255.0 UG 0 0 cipcb0
192.168.10.0 10.0.1.1 255.255.255.0 UG 0 0 cipcb0
I hoped to avoid the second case so I don't have to touch C when I add
another network to B.
I failed to mention that eth2 (and eth1 on C) have nothing to do with the
cipcb0 interfaces. These are actually used for the ADSL "modems".
Perhaps a little art will explain:
/---\
| A |
\___/
|
|
eth0=/---\
| B |=eth2-----[ADSL modem]
eth1=\___/ ||
| ppp0------------ Internet
| ||
/---\ cipcb0-----\
| Z | |
\___/ |
|
|
|
/---\ |
| E | cipcb0-----/
\___/ ||
| ppp0------------ Internet
| /---\ ||
*--eth0=| C |=eth1-----[ADSL modem]
| \___/
|
/---\
| D |
\___/
B eth0 is 192.168. 1.1 / 255.255.255.0
B eth1 is 192.168.10.1 / 255.255.240.0
C eth0 is 192.168. 2.1 / 255.255.255.0
B eth2 is 10.200.1.1 / 255.0.0.0
C eth1 is 10.200.1.1 / 255.0.0.0
(ADSL eth interfaces are set up from the adsl howto)
B cipcb0 is 10.0.1.1 / 255.255.255.255 P-t-P 10.0.1.2
C cipcb0 is 10.0.1.2 / 255.255.255.255 P-t-P 10.0.1.1
I think B-eth1 should be /255.255.255.0 instead of /20, as well as a route
to 192.168.0.0/20 by eth1. I did this, but no change.. no surprise.
At Henry's suggestion, I did a traceroute from E to A (D has a simi-broken
network setup, but still works.. I don't want to reinstall window right
now..). I get basically the reverse (from D or E)
traceroute to A
1 C (192.168.2.3) <10 ms <10 ms <10 ms
2 * * *
3 A (192.168.2.2) 62 ms 64 ms 58 ms
Again, ping works fine. I really don't know where to start with tcpdump
and how to look for path mtu discovery problems, but I supposed TIYFT
(tcpdump is your friend too). Tell me what to do/look for and I'll give
it a shot (I do have tcpdump).
-Cedar
On Tue, 4 Sep 2001, Dani Arbel wrote:
> Cedar,
> maybe you might have some path mtu discovery problem?
> try to tcpdump/ethereal on B and C and see what hapens.
>
> About the routing table:
> more specific routes has precedence when being looked on for routing, so
> the routing tables look ok (though may be simplified).
> Dani
>
> On Mon, 3 Sep 2001, Cedar Cox wrote:
>
> >
> > I'm not exactly sure what's going on here. This is the setup:
> >
> > A ==== B -------- C ==== D
> >
> > A, B, and C are running linux, D happens to be a running windows, if it
> > matters. The A-B link is ethernet, as is C-D. B-C is a CIPE link over
> > the internet (a VPN).
> >
> > A is 192.168.1.4
> > B is 192.168.1.1 and 10.0.1.1
> > C is 192.168.2.1 and 10.0.1.2
> > D is 192.168.2.2
> >
> > I have the default route on A pointing to B, on D pointing to C. On B I
> > have:
> >
> > Destination Gateway Genmask Flags Metric Ref Iface
> > 10.0.1.2 * 255.255.255.255 UH 0 0 cipcb0
> > 192.168.2.0 10.0.1.2 255.255.255.0 UG 0 0 cipcb0
> > 192.168.1.0 * 255.255.255.0 U 0 0 eth0
> > 192.168.0.0 * 255.255.240.0 U 0 0 eth1
> > 10.0.0.0 * 255.0.0.0 U 0 0 eth2
> > loopback * 255.0.0.0 U 0 0 lo
> >
> > On C I have:
> >
> > Destination Gateway Genmask Flags Metric Ref Iface
> > 10.0.1.1 * 255.255.255.255 UH 0 0 cipcb0
> > 192.168.2.0 * 255.255.255.0 U 0 0 eth0
> > 192.168.0.0 10.0.1.1 255.255.240.0 UG 0 0 cipcb0
> > 10.0.0.0 * 255.0.0.0 U 0 0 eth1
> > loopback * 255.0.0.0 U 0 0 lo
> >
> >
> > What I can't do is telnet from B to D (port 5800.. VNC), but I can telnet
> > from A to D. I'm not sure how I might have messed up my routing or
> > something else. Maybe it's my Genmask's. The "strange" thing is that I
> > can ping D from A or B without problem. A traceroute from A to D looks
> > like:
> >
> > traceroute to D
> > 1 B (192.168.1.4) 2.514 ms 1.572 ms 1.229 ms
> > 2 * * *
> > 3 D (192.168.2.2) 62.168 ms 64.307 ms 58.755 ms
> >
> > If this is not enough information, just say so and I'll give more. Maybe
> > I'll get creative and draw some ascii art of the big picture.. :)
> >
> > Thanks
> > -Cedar
> >
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