[TriLUG] OT: Traceroute / routing question

[Brian Henning]

Hi,

Someone who knows more about routing might be able to answer this for me.

At my office, our local LAN is on a subnet, let's call it 192.168.A.0/24.
At our parent office far away, their LAN is on a subnet let's call
192.168.B.0/24.
We have a hardware VPN (SonicWall endpoints) configured between the two.
The SonicWall devices are also our gateways.

What confuses me is that tracert tells me my .A machine can reach a .B
machine in one hop:

C:\Users\bhenning
Yes? tracert 192.168.B.xxx

Tracing route to 192.168.B.xxx
over a maximum of 30 hops:

  1    46 ms    46 ms    46 ms  192.168.B.xxx

Trace complete.

...but my local routing table does not seem to include specific routing for
.B:

IPv4 Route Table
===========================================================================
Active Routes:
Network Destination        Netmask          Gateway       Interface  Metric
          0.0.0.0          0.0.0.0   192.168.A.yyy     192.168.A.xxx     20
        127.0.0.0        255.0.0.0         On-link         127.0.0.1    306
        127.0.0.1  255.255.255.255         On-link         127.0.0.1    306
  127.255.255.255  255.255.255.255         On-link         127.0.0.1    306
      192.168.A.0    255.255.255.0         On-link     192.168.A.xxx    276
    192.168.A.xxx  255.255.255.255         On-link     192.168.A.xxx    276
    192.168.A.255  255.255.255.255         On-link     192.168.A.xxx    276
        224.0.0.0        240.0.0.0         On-link         127.0.0.1    306
        224.0.0.0        240.0.0.0         On-link     192.168.A.xxx    276
  255.255.255.255  255.255.255.255         On-link         127.0.0.1    306
  255.255.255.255  255.255.255.255         On-link     192.168.A.xxx    276
===========================================================================

What I don't understand is why doesn't tracert show the router (at
192.168.A.yyy) as a hop between me and the .B machine?  (If our netmask were
/16, I'd understand, but it's /24...)

For comparison, I just got an AT&T 3G MicroCell at home.  I put it on a
(logically but not physically) separate subnet from the rest of my LAN so
that I could firewall it off and lessen the possibility of AT&T snooping
around my network (a little paranoia never hurt anyone!).  I haven't set up
the firewall rules yet, so I can ping it from the rest of my LAN.  When I
tracert it, the router[1] DOES show up as a hop:

C:\Documents and Settings\brian>tracert 10.32.4.103

Tracing route to 10.32.4.103 over a maximum of 30 hops

  1   160 ms     1 ms     1 ms  192.168.0.80
  2     3 ms     3 ms     3 ms  10.32.4.103

Trace complete.

Why's there a difference?

Thanks for the enlightenment,
~Brian

[1] A Linux machine which serves both subnets from a single Ethernet
interface via virtual interfaces.

------------------------------------------------------ 
          Brian Henning, Software Engineer

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