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New Member

ospf cost on trunk

In the below given netwrok scenario, how would osfp work ?

Would it consider the L2 trunk between Switch B and Switch C when calculating the cost to router D?

so is the ospf cost from S/w A => S/w B =>Router D = 20 and

S/w A =>S/w C=>S/w => RouterD =20, or will ospf consider the cost on the trunk link too. The trunk between Switch B and Switch C is a L2 trunk and all the switches used in the network are Cat6509.

L3S/w A----------------

| +

| +

L3S/w B=======L3S/wC

|

|

Router D

7 REPLIES
Silver

Re: ospf cost on trunk

OSPF is a layer 3 protocol, it will not account dor the trunk. I will however take in to account the cost associated with the vlans in the layer 3 switch

New Member

Re: ospf cost on trunk

OSPF isn't layer 3 protocol...OSPF uses TCP 89 port to tran data......

Re: ospf cost on trunk

Not to nit-pick but OSPF is protocol 89. See link http://www.iana.org/assignments/protocol-numbers .

So OSPF won't care about the trunk itself, only the ospf cost of the link.

Steve

Bronze

Re: ospf cost on trunk

OSPF uses *IP* (not TCP) protocol 89.

In standard discussions regarding networking, "Layer-3" is presumed to mean Layer-3 (Network) within the ISO OSI Reference Model (Defined by the ISO in ISO/IEC 10731:1994) Layer-3 is the first layer with Network (in this case IP) Addresses. OSPF "rides" on IP, it uses IP addresses. OSPF is a layer-3 protocol.

If the tone of your message was not intended to be as hostile as it came out, I appoligize, otherwise possibly you should check the quality of the posts by others (eg deilert) before you post. If the quality of their previous posts has been high, you may want to consider double checking your facts before disagreeing.

Bronze

Re: ospf cost on trunk

I appoligize for the tone of my reply... The coffee hadn't sunk in yet...

Re: ospf cost on trunk

Warren, to whom are you writing this post?

I can't see any "hostile" remarks from anyone in this thread. Dave wrote it is a L3 protocol, Xiao disagreed saying it is L4, and I wrote saying it is protocol 89 (and from the link you can see it's running on IP), not TCP port 89. Hence I was agreeing with Dave.

I fail to see where the hostile remarks that you mention are coming from.

Steve

New Member

Re: ospf cost on trunk

I agree OSPF is a Layer 3 'routing' protocol as opposed to 'routed' (IP Protocol #89). The OSPF will use the Layer 3 link cost calculated from your reference bandwidth. Although when using Native IOS & Layer 3 Port channels it does dynamicaly adjust the cost dependant on how many links are Layer 3 up etc

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