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some notes about BGP, OSPF/IS-IS, RIP/EIGRP | www.comrite.com
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some notes about BGP, OSPF/IS-IS, RIP/EIGRP

BGP:

run on tcp 179, path vector protocol,  65K routes
eBGP: append AS_PATH

iBGP:  ( the same AS number),  iBGP need full mesh,

thus could use Route Reflector (RR, need to config, not like OSPF DR/BDR is auto-elected), up to 10-20 iBGP routers

BGP conferderation ( multiple private AS number in internal network, but public AS to outside ), could >20 iBGP routers

show ip bgp:

network next hopt path

x                ip1    34 45 59

x               ip2     23  45   ( thus will be choosen  to go to x, as the AS_PATH is shortest)

sample config for BGP confederation

router bgp 65002 ( private as number)

bgp confferation identifier 600 ( public AS number)

bgp conferation peers 65003 ( internal iBGP peer)

neight  1.1.1.1 remote-as 500

neight 2.2.2 remote-as 65001

network 20.0.0.0

 

OSPF

link-state IGP procotol (within one AS), has its own protocol 89, thoursands of routes?

should have area 0 ( backbone), other additional areas should have a direct or virtual link with this backbone area by ABR

ABR (area border router) : will main seperate link state db for each area, and maintain summarized routes for all areas

DR, BDR for each multi-access segment not per area, will be auto-elected. non DR/BDR router will exchange only with DR/BDR. DR will distribute topology info to every other router inside the same area.

OSPF LSA:
Type1 – Router – router announcing itself and lists links to other routers with metrics in the same area
Type2 – Network – lists what routers are connected by the broadcast segment.
Type3 – Net Summary – An Area Border Router summarizes one area, and sends it to other areas
Type4 – ASBR Summary – An ASBR summarizes external routes that are injected from another routing protocol
Type5 – AS External – Full network routes imported from other routing protocols
Type6 – Group Membership – A multicast advertisement that is not used in OSPFv3
Type7 – NSSA External – Routers in a not so stubby area (NSSA) send external routing information to the ABR to be redistributed (as type 5s to other areas)

stub area: s  allows Type 2 and Type 3 LSAs. Type 5 LSAs are not passed into the area. A default route is also passed in from the ABR.

totally stubby area: Only Type 2 LSAs and a default route are passed into the area (although technically the default route is a type 3… but that is the only one).

Not-So-Stubby Areas. NSSAs have Type 2, Type 3, and Type 7 LSAs. areas, but not have other area’s external routes imported into this area. In other words, local external routes are allowed, but not external routes from other areas. The ABR changes the Type 7 into a Type 5 when it passes it to other areas.

sample configure:

router ospf 1 # process number

network 192.168.1.0 0.0.0.255 area 0 ( wildcard mask)

network 1.1.1.0 0.0.0.3 area 0

 

EIGRP

distance-vector+link-state  ( hundreds of routes) , no tcp/udp, but use cisco RTP

it is AS number is totally different from BGP AS number, only send incremental updates

ample config:

router eigrp 100 ( AS number, should be the same for all the routers in this AS)

no auto-summary ( avoid problems)

network x.x.x.x wild-mask

network y.y.y.y wild-mask

 

useful comamnds:

show ip prootocol

show ip route

show ip eigrp neight

show p eigrp toplogy ( feasible routes)

 

 

 

 

References:

http://ciscocertstudyblog.blogspot.com/2010/06/ospf-area-types-stub-totally-stubby-not.html

https://supportforums.cisco.com/document/127851/routing-protocol-selection-guide-igrp-eigrp-ospf-bgp

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