Network Security Blog

Type=Path Vector

Algorithm=Path Selection

eBGP AD=20

iBGP AD=200

Protocols IP

Transport TCP 179

####WLAOM..RCN###

attributes:
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1.weight (default=0) prefered=highest

configure this on a router that is receiving the routes (IN)  (customer side)

cisco proprietary
this is given on specific device

is given on PA it self..

#neighbor X.X.X.X weight 762

2.local preference(default=100)prefered=highest

R1#bgp default local-preference 200

but if we give above command it applies for all routes

Note that the Local Preference will only affect the traffic leaving the AS.
you can use route maps to apply local preference for specific routes.

access-l permit 10 10.10.10.1
access-l permit 20 50.0.0.1
R1#route-map FILTER_10
match ip add 1
set local-preference <high>

R1#router bgp <>
neighbour <neighbor ip> route-map FILTER_10 in

only in is supported, routes learning in to our AS

3.Locally Originated prefered=local routes

- Prefer the path that was locally originated via a network

4.AS PATH prefered=lowest

R1---R2_10----R3_30

# neighbor <ISP1> route-map RMAP out

route-map RMAP permit 10

 match ip address 1

 set as-path prepend 11 11 11 <---should be our own AS number

ISP side:-

we want to use ISP1 as backup so increased AS pasth prepend to 1 1 1 1 1. so far good..

BUT ISP1 is also clever. they always follow Customer link>>>Peer LINKS>>>UPSTREAM OTHER ISP's

because they want to charge for Link.

so even though we use AS path. ISP1 will use Local preference as follows

Customer Link=LP=100

Peer Link=LP=80

Upstream ISP=LP=50

5.ORIGIN  prefered=prefered=lowest origin IGP<EGP<Icomplete
-IGP advertised through BGP network command

-EGP routes came through redistribution

6.MED(Multi exit discriminator)==(Lowest preferred)default=0

.

7)EBGP are preffered than IBGP.

8)Lowest IGP metric:-

BGP internal routing, i.e;IGP. used in MPLS or internal network.

9)Maximum Paths:-

checkes if loadbalance is there for multiple BGP paths.

IF not it continue to next one.

10)Oldest one(External):-first come first serve

11)router-ID==prefered=lowest

- If router id is also same then it uses below one

12)cluster list length ==prefered=lowest
-used in route reflector environmnt

13)neighbor address==prefered=lowest

####WLAOM..RCN###

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