From: jona@iscp.bellcore.com (Jon Alperin)
Subject: Highly available network routing (LONG POST)
Organization: Bellcore
Distribution: usa
Date: Fri, 16 Oct 92 13:44:12 GMT
Keywords: RIP, ARP, netstat

Morning (at least it is for me...)

 I have several questions about TCP/IP RIP Routing, involving cisco
routers and IBM's AIX operating system (However, I will try to keep
things general in nature). I would appreciate e-mail replies to 
'jona@iscp.bellcore.com', as I do not normally read all these newsgroups.
I will summarize results for anyone interested.

 I have been involved in building a highly available internetwork to 
support continuous operability between various applications executing
on separate systems. The network itself is a ring topology of T1 links
connecting Cisco routers, and the routers themselves connect to the same
end networks:


           +====R1 ------------ R2==+
      S1 --|       \          /     |- S2
           |        \        /      |  
           +====r4 __\______/_ r5 ==+
                   \  \    / /
                    \   R3  /
                     \  |  /
                      \ | /
                        r6--- s3

The idea is that S1 (System 1) will always have a communication path with
S2, even if a network link or router is lost. R3 and R6 will connect to various
other systems. All S1 and S2 systems are running routed with a -q option.

All networks are given a class B address (e.g. 160.190), but the network mask
is 255.255.255.0 so that sunbetting is enabled. The cisco routers show
160.190.0.0 is subnetted into more than 18 subnets (due to the other systems
and networks which I did not show...). However, on S1 and S2 (both AIX V3.2.2
boxes), a netstat -r shows the following:

Routing tables
Destination      Gateway            Flags  Refcnt Use       Interface

Route Tree for Protocol Family 2:
(root node)
127              localhost          U           3     2799  lo0
160.190          160.190.100.100    UG         19     9886  tr0
[plus a route for the local interfaces...]

instead of each of the 18 routes. The gateway address cooresponds to 
only 1 router (R1 or R2) at any given time, even though I know the hop
count to a system (s3) hanging directly off r6 (and _not_ connected to r3)
should be less coming from r4 than from R1. yet r4 never shows up in the
routing table.

 Is this the expected result? Could it be that AIX is having a problem with
class B addresses and not picking the routes from the RIP updates?

 Also, when we do establish a connection (like a ping) between S1 and S2, 
sometimes we see a UGHD route directly to the host, with netstat reporting the
160.190.subnet.host address, so it obviously is simply truncating to a class
B network.

 The broadcast address on the systems is 160.190.subnet.255, and the
router uses all 1's for its broadcast (which is equivalent, right?).

When we disconnect a router R2, we expect that the S2 systen will pick
up routes from r5 after 90 seconds (30 to recieve a rip update,
30 for stale marked partitions, and 30 for deletion). However, it 
actually appears to take 4 minutes (or longer)
for this to occur. Can anyone account
for this time lag? Could it be because the aix system does not see each of
the subnets individually?

 On a slightly related note, when we disconnected the cisco token ring
interface from one of the lans, it turned the interface off (i.e. down), and
requires manual access to the router to re-initialze via a 'clear interface'
command. Can this be changed to always stay active (wellfleet does stay active, 
and simply logs wire faults...)? And when we reconnected the router (after the 
other router had been established as the network connection), the netstat
reported route switched back to this router (as if it were some sort of
primary router)...why?

 Any help would be greatly appreciated. Once again, please e-mail replies.

 Thanks,

 jon


-- 
Jon Alperin - Bellcore
---> Internet: jona@iscp.bellcore.com
---> Voicenet: (908) 699-8674

* All opinions and stupid questions are my own *

"I don't have any experience running up a 4 trillion dollar debt" - Ross Perot
"If there's a fair way, I'm all ears" - Ross Perot
Newsgroups: comp.unix.aix