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BGP NLRI can be originated by
- network statements
- require an exact match in the routing table
- redistribute statement
- fairly standard redistribution one of things to watch out for by default it
will not redistribute ospf external you need to manually tell it to
redistribute ospf external routes
- agregate-address statement
-requires at least one subnet in the BGP table first
- BGP Inject MAP statement
- opposite of Aggregation
BGP Network Statement
----------------------
- Originates prefixes with origin of IGP (i)
- Requires exact match in the routing table
- does not have to be connected prefix can be learned via IGP
-without adding the mask keyword it will asssume a classfull mask
sh ip bgp regexpr ^$ - shows you network generate in local AS can be useful for
verifying network statement
When you do a network statement you may see different metric values in metric/med
field. This is basically because it will bring in the IGP originated route
metric/cost into BGP for connected routes the metric is zero. THe med value is non
transitive value when you send this to other AS it will not be carried in the update.
BGP Redistribute Statement
---------------------------
Origin prefixes with origin code of incomplete (?)
Originates classfull summary if auto summary is enabled
AUtomatically carries the IHP metric to the med field of the BGP update
It will not redistribute ospf external by default
redistribute ospf "pid" match internal external
TO be redistributed as normal the route has to be in the routing table
NO seed metric is required as IGP metric is inherited
You can filter redistribution
for example
ip prefix-list EIGRP-TO-BGP permit 10.10.10.0/24
router-map EIGRP-TO-BGP
match ip address prefix-list EIGRP-TO-BGP
router bgp 100
redistribute eigrp 4 route-map EIGRP-TO-BGP
sh ip bgp | in /? - will give a list in the bgp table of incomplete routes
LAB
----
For the LAB we have multiple AS i will start by putting a few routes into the bgp
process
I will use the network statement to inject the routes for AS 100 loopback so r6,r4,r1
we will do this on r1
r1(config)#router bgp 100
r1(config-router)#network 6.6.6.6 mask 255.255.255.0
% BGP: Incorrect network or mask configured
r1(config-router)#network 6.6.6.6 mask 255.255.255.255
r1(config-router)#network 4.4.4.4 mask 255.255.255.255
r1(config-router)#network 1.1.1.1 mask 255.255.255.255
r1(config-router)#
I tried to inject 6.6.6.6 it with a incorrect mask and it threw up an error
r1#sh ip bgp
BGP table version is 8, local router ID is 1.1.1.1
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,
r RIB-failure, S Stale
Origin codes: i - IGP, e - EGP, ? - incomplete
Network Next Hop Metric LocPrf Weight Path
*> 1.1.1.1/32 0.0.0.0 0 32768 i
*> 4.4.4.4/32 155.0.146.4 156160 32768 i
*> 6.6.6.6/32 155.0.146.6 156160 32768 i
if we look at r1 sh ip bgp
we have all the routes in the bgp table notice the metric is different
for the connected route 1.1.1.1 it defaults to metric/med defaults to 0.0.0.0 also
the next hop is local 0.0.0.0
for the non-connected recieved from other hosts we are learning the routes via eigrp
we inherit the metric from eigrp of 156160 we do see the relevant next hops
if we notice on r3 we are recieving the routes
r3#sh ip bgp
BGP table version is 62, local router ID is 3.3.3.3
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,
r RIB-failure, S Stale
Origin codes: i - IGP, e - EGP, ? - incomplete
Network Next Hop Metric LocPrf Weight Path
*> 1.1.1.1/32 1.1.1.1 0 0 100 i
*> 4.4.4.4/32 1.1.1.1 156160 0 100 i
*> 6.6.6.6/32 1.1.1.1 156160 0 100 i
on r2
------
r2#sh ip bgp
BGP table version is 25, local router ID is 12.12.12.12
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,
r RIB-failure, S Stale
Origin codes: i - IGP, e - EGP, ? - incomplete
Network Next Hop Metric LocPrf Weight Path
*> 1.1.1.1/32 5.5.5.5 0 400 300 100 i
*> 4.4.4.4/32 5.5.5.5 0 400 300 100 i
*> 6.6.6.6/32 5.5.5.5 0 400 300 100 i
r2#
the metric is gone it is non transitive parameter so we do not recieve
notice at the end we have i this is the origin code of igp which is preference to a
redistribute route
if we had received other routes from other AS this command would filter down to the
local
r1#sh ip bgp regexp ^$
BGP table version is 8, local router ID is 1.1.1.1
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,
r RIB-failure, S Stale
Origin codes: i - IGP, e - EGP, ? - incomplete
Network Next Hop Metric LocPrf Weight Path
*> 1.1.1.1/32 0.0.0.0 0 32768 i
*> 4.4.4.4/32 155.0.146.4 156160 32768 i
*> 6.6.6.6/32 155.0.146.6 156160 32768 i
BGP Redistribution
-------------------
we will try redistributing routes from r4
s4(config)#router bgp 400
s4(config-router)#redistribute eigrp 1
s4(config-router)#exit
s4(config)#exit
notice we do not need specify a metric as it will inherit a metric
s4#sh ip bg
01:53:53: %SYS-5-CONFIG_I: Configured from console by consolep
BGP table version is 111, local router ID is 2.4.4.4
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,
r RIB-failure, S Stale
Origin codes: i - IGP, e - EGP, ? - incomplete
Network Next Hop Metric LocPrf Weight Path
*> 1.1.1.1/32 155.0.108.2 2300672 32768 ?
*> 2.1.1.1/32 155.0.108.2 2305792 32768 ?
*> 2.2.2.2/32 155.0.108.2 2300672 32768 ?
*> 2.3.3.0/24 155.0.108.2 2306048 32768 ?
*> 2.4.4.4/32 0.0.0.0 0 32768 ?
*> 3.3.3.3/32 155.0.108.2 2300672 32768 ?
*> 4.4.4.4/32 155.0.108.2 2300672 32768 ?
*> 5.5.5.5/32 155.0.108.2 143616 32768 ?
*> 6.6.6.6/32 155.0.108.2 2303232 32768 ?
*> 12.12.12.12/32 155.0.108.2 2300672 32768 ?
*> 22.2.2.0/24 155.0.108.2 143360 32768 ?
*> 155.0.0.0/24 155.0.108.2 2172672 32768 ?
*> 155.0.13.0/24 155.0.108.2 2684672 32768 ?
*> 155.0.23.0/24 155.0.108.2 2684672 32768 ?
*> 155.0.45.0/24 155.0.108.2 2172672 32768 ?
*> 155.0.58.0/24 155.0.108.2 15616 32768 ?
*> 155.0.67.0/24 155.0.108.2 2177792 32768 ?
Network Next Hop Metric LocPrf Weight Path
*> 155.0.79.0/24 155.0.108.2 2178048 32768 ?
*> 155.0.108.0/24 0.0.0.0 0 32768 ?
*> 155.0.146.0/24 155.0.108.2 2175232 32768 ?
s4#
notice the origin code is ? which stands for incomplete this is redistributed routes
notice all the different metrics that have been inherented from the IGP
we could filter this down so we do not advertise all the routes say all we want to
advertises is 155.0.79.0/24
we firstly create a prefix-list to match the route
s4(config)#ip prefix-list INTOBGP permit 155.0.79.0/24
and then a route-map
s4(config)#route-map EIGRPTOBGP permit 10
s4(config-route-map)#match ip address prefix-list INTOBGP
s4(config)#router bgp 400
s4(config-router)#no redistribute eigrp 1
s4(config-router)#redistribute eigrp 1 route-map EIGRPTOBGP
s4(config-router)#
s4#sh ip bgp
BGP table version is 141, local router ID is 2.4.4.4
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,
r RIB-failure, S Stale
Origin codes: i - IGP, e - EGP, ? - incomplete
Network Next Hop Metric LocPrf Weight Path
*>i1.1.1.1/32 1.1.1.1 0 100 0 100 i
*>i4.4.4.4/32 1.1.1.1 156160 100 0 100 i
*>i6.6.6.6/32 1.1.1.1 156160 100 0 100 i
*> 155.0.79.0/24 155.0.108.2 2178048 32768 ?
s4#
we are recieving the routes from r1 but otherwise we are only advertising
155.0.79.0/24
s4#sh ip bgp neighbors 5.5.5.5 advertised-routes
BGP table version is 144, local router ID is 2.4.4.4
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,
r RIB-failure, S Stale
Origin codes: i - IGP, e - EGP, ? - incomplete
Network Next Hop Metric LocPrf Weight Path
*> 155.0.79.0/24 155.0.108.2 2178048 32768 ?
Total number of prefixes 1
s4#
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