Subnet Routing Config

Unanswered Question
Mar 18th, 2007

I have a confusion regarding subnet routing.

2 branches connected to main site via private wireless network each with own gateway.

Branch 1: 172.16.10.x

Branch 2: 172.16.20.x

1. What mask should be used? 255.255.0.0 or 255.255.255.0? What differences other than host limitation would it make?

2. What routes should be entered into main site router (2801) based on the above?

3. On a separate note, say I choose a mask of 255.255.0.0. What would routing decision would the main site router take for a traffic to destination 172.16.10.1?

thx

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glen.grant Sun, 03/18/2007 - 02:53

It should be a /24 mask the way you show it . If you use a /16 then this would include anything in the 172.16 and make it one huge network and thus you could not break it up the way you show it because technically they would both be in the same subnet with a /16 mask. . You don't say how your network is setup and what routing protocols you are using . To eliminate any subnetting problems use 255.255.255.0 for your mask .

rsabapathee Sun, 03/18/2007 - 03:06

thx for reply.

main site: cisco 2801.

branches: cisco 1841

all link via private wireless network.

Static Routing configured.

any ideas on third question. say i go for mask 255.255.255.0. static routing configured as follows on main site router:

ip route 172.16.10.0 255.255.0.0 "branch1 gateway"

ip route 172.16.20.0 255.255.0.0 "branch2 gateway"

traffic is meant for 172.16.10.1. what routing decision will main site router take in this scenario?

Jon Marshall Sun, 03/18/2007 - 03:12

Hi

You don't say what your main siet subnet is but from your question static routing would work fine here.

You ip route statements are fine and the main site router will always choose the longest match in it's routing table so anything destined for 172.16.10.x should be sent to branch 1.

If the branches need to communicate with each other and they go via the main site just use a default route at each branch site pointing back to the main site router.

HTH

Jon

mahmoodmkl Sun, 03/18/2007 - 03:10

Hi

It depends upon the rouitng protocol u r using.If u r using a classful routing protocol then u may face routing issues,if u r using classless routing protocol then u will be fine.

Thanks

Mahmood

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