General Querries -1

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Apr 26th, 2009
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Hello Freinds,


I am beginer in this cisco field. So time by time i would like to put my querries with all you experts for your suggestions and guidance.



Question 1) What is Adminstrative Distance of BGP.(including IGP & EGP both).


Question 2) Which is the best protocol between EIGRP and OSPF and why ?


Question 3) In MPLS which thing/router is responsible for forwarding vrf labels.


regards


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Laurent Aubert Sun, 04/26/2009 - 09:52
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Hi,


Welcome to Cisco world ;-)


1) eBGP: 20, iBGP: 200


More info:

http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a0080094195.shtml


2): There is no really best protocol. Each one has its pros&cons that must be compare to your context and requirements.


EIGRP is usually more easy to deploy than OSPF and by default converge faster but is Cisco proprietary so all your routers must be Cisco boxes.


More info:

http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a0080093f07.shtml


http://www.cisco.com/en/US/tech/tk365/technologies_white_paper09186a0080094e9e.shtml


3) If you mean VPN Labels by vrf labels, then it's MP-BGP which runs between PE routers. IGP Labels are exchanged via LDP between PE and P routers. P routers don't need to know about the VPN label.


HTH


Laurent.

cisco.net Sun, 04/26/2009 - 23:01
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Thanks a lot..! ! ! laurent



For MPLS labels i was meant from MPLS labels only.


For eg:- vrf ABC


Here ABC is label. and i need to know what all are reposible for forwarding this label from hop to next hop.

Laurent Aubert Mon, 04/27/2009 - 09:52
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  • Cisco Employee,

Hi,


I'm not sure to follow you. Labels are associated to ip prefixes. If this prefix is part of a VRF then MP-BGP will allocate the label called VPN label. If the prefix is part of the global routing table (GRT), then LDP will allocate the label.


When a packets is received on a VRF interface the following happens:


1- PE make a route lookup in the VRF to find the next-hop.

2- if the next-hop is another PE, two labels will be added to this packet: one IGP label associated to the next-hop address (learned from LDP) and a VPN label learned from the remote PE via MP-BGP

3- P routers use only the IGP label to forward the packet to the remote PE


4- Remote PE receives it, analysis/removes the VPN label and send it to the outgoing interface associated to this label


HTH


Laurent.

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