Default router in our two subnetworks

Ray Ballisti, October 2001


  Content:
  1. Subnetting
  2. Default router
  3. Redundancy and availability

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Subnetting

The whole ETH is subnetted: 129.132.aa.bb
( we say it is a Class B network: 129.132.0 )

For more information about IP routing, gateways and subnetting: click here

We have now in our Institute IFH two subnets:

SubnetIP numberRange
(IP's last number)
ifh129.132.20.0 1 < xx < 127
mwel-pc129.132.20.128 129 < yy < 254

 

Default router

The first number in the host-range in a subnet is always the default router:

SubnetDefault router
ifh 129.132.20.1
mwel-pc129.132.20.129

 

Redundancy and availability

To add some redundancy and thus have an higher availability of the network our Communication Services use the "hsrp" system: we have in each subnet TWO routers with the higher IP number of the range. One of them take the identity of the default router thus leaving the other one free for maintenance, upgrades etc.
Thus don't be surprise if you see that your machine is actually using another router than the default one.

Routers in our subnets:

subnetrouter IProuter name
ifh129.132.20.1  rou-etx-1-ifh-hsrp.ethz.ch  (DEFAULT)
ifh129.132.20.125  rou-etx-1-ifh.ethz.ch
ifh129.132.20.126  rou-etx-2-ifh.ethz.ch
   
mwel-pc129.132.20.129  rou-etx-1-mwel-pc-hsrp.ethz.ch  (DEFAULT)
mwel-pc129.132.20.253  rou-etx-1-mwel-pc.ethz.ch
mwel-pc129.132.20.254  rou-etx-2-mwel-pc.ethz.ch

Example: 

root@deneb:~# netstat -r

Routing Table: IPv4
  Destination           Gateway            Flags  Ref   Use   Interface
--------------------  -------------------  ----- ----- ------ ---------
bigbang                bigbang-mwel          UGH    1   8784  
ifh.ethz.ch            deneb                 U      1 230171  eri0
BASE-ADDRESS.MCAST.NET deneb                 U      1      0  eri0
default                rou-etx-1-ifh.ethz.ch UG     1   9559  
localhost              localhost             UH     1 2080492  lo0

The "Routing Table: IPv6" has to do with the new enhanced IP protocol: don't care about it now.
 

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