BGP attributes V/S BGP Comunity

Have a small doubt : what is the difference between BGP attributes AND BGP Communities ?

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Posting
It's really up to the two parties, sharing community values, to determine how they wish to use them and what a particular community value means. Some what commonly, the top half of a community value represents the AS the community is for and the bottom half of the community is a weight to apply to route. (I.e. communities are often used to manipulate how traffic will be routed.)
I also want to mention, more than one community might be attached to a route prefix.

Similar Messages

BGP decision algorithm nitty-gritty (relationship of locally originated routes to weight attribute)

Hello everyone, i have a question on this algorithm. Specifically the relationship between (cisco specific) WEIGHT which is right at the top of the path selection algorithm.... and routes that are ORIGINATED_LOCALLY (3rd one down, after weight and local_pref).
Heres the relevant steps of the decision tree:
1/WEIGHT (highest wins)
2/LOCAL_PREF (highest wins)
3/ORIGINATED LOCALLY (prefer locally originated over peer learnt)
Whats confusing to me is that Jeff's book tells us that if a prefix is ORIGINATED_LOCALLY (ie entered into BGP on that same router - either by a network/aggregate-address statement, or from redistribution) then its WEIGHT will also be set to 32768 (as opposed to a BGP peer learnt route whose WEIGHT is set to 0). I understand this.
My question is why??? Seems to me that if this is the case there is little purpose of having ORIGINATED_LOCALLY in the decision tree at all, as the logic will never get there on account of the the propagation of its value into (the higher up) WEIGHT decision. This also in turn means that ORIGINATED_LOCALLY has the power to override the attribute LOCAL_PREF.... so couldn't this whole logic be simplified to be:
1/WEIGHT or ORIGINATED LOCALLY
2/LOCAL_PREF (highest wins)
This very thing has confused another user on another post too, that user writes: "I tried thinking of an example where "ORIGINATED LOCALLY" works but weight doesn't, but couldn't think of any."
looking forward to the thoughts of this community.
Thanks in advance, Keiran.
PS> perhaps the attached diagram will help visualise this.

Thanks for your reply shaikhkamran123, i hadn't considered the multivendor environment (where cisco specific concept of 'weight' would be irrelevant to those routers), so yes their decision would start with:
1) Local Preference
2) Locally originated
as opposed to cisco
1/WEIGHT (highest wins)
2/LOCAL_PREF (highest wins)
3/ORIGINATED LOCALLY (prefer locally originated over peer learnt)
but it still doesn't really explain why cisco chose to alter their inbuilt weight based on if a route was locally originated. This alters the logic of the above decision algorithm: ie if its locally originated, it will set a high weight (32768), which will be preferred.... and heres the main thing *BEFORE* local_pref is even looked at. So in other words decision criteria#3, gets merged into #1, skipping ahead of #2. Am i going crazy here??
thanks in advance all...
K.

Can i add my own bgp attribute as transistive and optinal

Hi
i need requirement to carry own bgp attribute in bgp update message , is it possible to add own bgp attributed using extended community
to carry one ipv4 address per vrf using bgp .
PE1----------PE2
vrf1 vrf2
1.1.1.1 2.2.2.2
i want to carry 1.1.1.1 in bgp update message to PE2 and carry 2.2.2.2 to PE1 using bgp update message per vrf .
Thanks
Duraipandi

Hi, Sergio gave the answer.
Here is a usefull link to go a step forward with JavaScript :
http://blogs.msdn.com/b/sharepointdev/archive/2011/04/14/using-the-javascript-object-model-in-a-content-editor-web-part.aspx
Fabrice DG, Technical Solutions Professional, EMEA at
AvePoint
Follow my technical blog (french).
Please remember to click "Mark As Answer" if a post solves your problem or "Vote As Helpful" if it was useful.

BGP attribute-download

Hi all,
did you know about bgp attribute-download :
http://www.cisco.com/en/US/docs/ios_xr_sw/iosxr_r3.2/routing/command/reference/rr32bgp.html#wp2809802
this command "bgp attribute-download" is required to activate the netflow to include the as number information on the netflow.
does the command will reset the BGP peering connection?
Thanks a lot,
Budi L

Hi Budi,
possibly you hit the
CSCtf80648
BGP attribute ID limited to 64K in 3.8.3, routes without attribute ID
fixed in 3.9.2, 4.0.0 and 4.1.0 releases.
If you are running 3.8.3 you may consider to have a SMU activated for this issue.
If you are running 4.0.0 and still getting this message please be aware
that in 4.0.0 BGP increased the max supported
attributes from 2^16 to 2^20 , and the FIB can only handle 2^16
attributes in hardware, thus with your full internet routing table you
were exceeding the attribute index database maximum of 65536. In 4.0.1,
the FIB index space is increased to 2^18 to increase the attribute space
to 256K.
I can recommend to open a TAC SR to verify what exactly happen in your case.
wbr
/vadim

BGP Weight Attribute

Guys,
I just need some clarification on the use of the bgp weight attribute. Let us say I have this setup. If both R1 and R2 are receiving the same set of routes from R3-R6, can I use weight attribute to influence the received routes so that R1 will have the best routes? Does weight works on different AS?

Absolutely. Cisco Freak and Jon Marshall are correct.
Also, you cannot compare between BGP attributes if R1 and R2 are not BGP peers. If you want to take complete control of routes being advertised by R3, R4, R5 and R6, you would be in better position if you run iBGP between R1 and R2.
Once BGP starts to run between R1 and R2, they both will get information about routes advertised by R3, R4, R5 and R6 and you will be able to reap many benefits of BGP protocol.
Peace and health,
Ravindra

Influencing BGP attributes within MPLS network

pls take a look at my question and diagram is attached in the file. pls help me to fix this problem.
I have following requirement about traffic paths within the
MPLS network.MPLS network is running MP-BGP4.
1.Traffic from Europe branch to Asia branch go through London
router.
2.Traffic from America branch to Asia branch go through Los Angeles
router.
3.The two paths through London and Los Angeles should have redundancy.
That is if path through London is not accessible all the traffic must
go through Los Angeles. IF Los Angeles path go down all the traffic must
go through London.
4.Traffic from Asia to Europe and America is controlled by redistributing
BGP4 learned routes with different metrics at the London and Los Angeles
routers.So that trafic from Asia branch to Europe go through London and
traffic from Asia to America go through Los Angeles.
I have been using below configs on the PE routers. But it is not working.
In the MPLS network only one path is selected for both traffic from Europe
and America.Pls can anyone help me to fix this problem.
#PE3
ip vrf CUSTOMER
rd 1:10
route-target export 1:20
route-target import 1:40
export map EXPORT-ROUTE
import map IMPORT-ROUTE
interface FastEthernet0/0
description LONDON-GW
ip vrf forwarding CUSTOMER
ip address 1.1.1.2 255.255.255.252
router bgp 65400
address-family ipv4 vrf CUSTOMER
redistribute connected
neighbor 1.1.1.1 remote-as 65401
neighbor 1.1.1.1 activate
neighbor 1.1.1.1 next-hop-self
neighbor 1.1.1.1 soft-reconfiguration inbound
no auto-summary
no synchronization
exit-address-family
ip extcommunity-list 1 permit rt 1:10
ip extcommunity-list 2 permit rt 1:40
route-map EXPORT-ROUTE permit 10
description LONDON-GW
match extcommunity 1
set extcomm-list 1 delete
set extcommunity rt 1:20 additive
route-map IMPORT-ROUTE permit 10
description EU & US-BRANCH
match extcommunity 2
#PE4
ip vrf CUSTOMER
rd 1:10
route-target export 1:30
route-target import 1:40
export map EXPORT-ROUTE
import map IMPORT-ROUTE
interface FastEthernet0/0
description LA-GW
ip vrf forwarding CUSTOMER
ip address 2.2.2.2 255.255.255.252
router bgp 65400
address-family ipv4 vrf CUSTOMER
redistribute connected
neighbor 2.2.2.1 remote-as 65402
neighbor 2.2.2.1 activate
neighbor 2.2.2.1 next-hop-self
neighbor 2.2.2.1 soft-reconfiguration inbound
no auto-summary
no synchronization
exit-address-family
ip extcommunity-list 1 permit rt 1:10
ip extcommunity-list 2 permit rt 1:40
route-map EXPORT-ROUTE permit 10
description LA-GW
match extcommunity 1
set extcomm-list 1 delete
set extcommunity rt 1:30 additive
route-map IMPORT-ROUTE permit 10
description EU & US-BRANCH
match extcommunity 2
#PE1
ip vrf CUSTOMER
rd 1:10
route-target export 1:40
route-target import 1:20
route-target import 1:30
export map EXPORT-ROUTE
import map IMPORT-ROUTE
interface FastEthernet0/0
description EU-BRANCH
ip vrf forwarding CUSTOMER
ip address 3.3.3.2 255.255.255.252
router bgp 65400
address-family ipv4 vrf CUSTOMER
redistribute connected
redistribute static
no auto-summary
no synchronization
exit-address-family
ip route vrf CUSTOMER 172.16.1.0 255.255.255.0 FastEthernet0/0 3.3.3.1 name EU-BRANCH
ip extcommunity-list 1 permit rt 1:10
ip extcommunity-list 2 permit rt 1:20
ip extcommunity-list 3 permit rt 1:30
route-map EXPORT-ROUTE permit 10
description EU-BRANCH
match extcommunity 1
set extcomm-list 1 delete
set extcommunity rt 1:40 additive
route-map IMPORT-ROUTE permit 10
description LONDON-GW(MAIN)
match extcommunity 2
set metric 100
route-map IMPORT-ROUTE permit 20
description LA-GW(BACKUP)
match extcommunity 3
set metric 200
route-map IMPORT-ROUTE permit 30
description OTHER
#PE2
ip vrf CUSTOMER
rd 1:10
route-target export 1:40
route-target import 1:20
route-target import 1:30
export map EXPORT-ROUTE
import map IMPORT-ROUTE
interface FastEthernet0/0
description US-BRANCH
ip vrf forwarding CUSTOMER
ip address 4.4.4.2 255.255.255.252
router bgp 65400
address-family ipv4 vrf CUSTOMER
redistribute connected
redistribute static
no auto-summary
no synchronization
exit-address-family
ip route vrf CUSTOMER 192.168.1.0 255.255.255.0 FastEthernet0/0 4.4.4.1 name US-BRANCH
ip extcommunity-list 1 permit rt 1:10
ip extcommunity-list 2 permit rt 1:20
ip extcommunity-list 3 permit rt 1:30
route-map EXPORT-ROUTE permit 10
description US-BRANCH
match extcommunity 1
set extcomm-list 1 delete
set extcommunity rt 1:40 additive
route-map IMPORT-ROUTE permit 10
description LONDON-GW(BACKUP)
match extcommunity 2
set metric 200
route-map IMPORT-ROUTE permit 20
description LA-GW(MAIN)
match extcommunity 3
set metric 100
route-map IMPORT-ROUTE permit 30
description OTHER

Hi Manoj
"send-community both" will export both Standard and Extended Communities
The Standard Community Values which we are setting up New on PE3 and PE4 and Matching on PE1 and PE2 can be anything in ASN:nn Format..I Just randomly chose them as 65400:1111 on PE3/PE1 and 65400:2222 on PE4/PE2.
The extcommunity values to be used on PE3/PE4 will be the export RT values used in the VRF Customer Config as posted in your first post..
#PE3
ip vrf CUSTOMER
rd 1:10
route-target export 1:20
route-target import 1:40
export map EXPORT-ROUTE
import map IMPORT-ROUTE
#PE4
ip vrf CUSTOMER
rd 1:10
route-target export 1:30
route-target import 1:40
export map EXPORT-ROUTE
import map IMPORT-ROUTE
I think I mixed up little with PE3 as PE1 and PE4 as PE2 instead ..Revised corrected config would be
On PE3-- Under VPNv4 We enable sending out the normal community values out to the RR.Then we match the extcommunity rt for the VRF Customer and set the community value to 65400:1111 which will be matched at PE1
router bgp 65400
address-family vpnv4
neighbor "RR-IP" send-community both
neighbor "RR-IP" route-map community out
exit-address-family
route-map community permit 10
match extcommunity CUSTOMER
set community 65400:1111
route-map community permit 20
ip extcommunity-list standard CUSTOMER permit rt 1:20
On PE4-- Under VPNv4 We enable sending out the normal community values out to the RR.Then we match the extcommunity rt for the VRF Customer and set the community value to 65400:2222 which will be matched at PE2
router bgp 65400
address-family vpnv4
neighbor "RR-IP" send-community both
neighbor "RR-IP" route-map community out
exit-address-family
route-map community permit 10
match extcommunity CUSTOMER
set community 65400:2222
route-map community permit 20
ip extcommunity-list standard CUSTOMER permit rt 1:30
On PE1-- Under VPNv4 We match the community value 65400:1111 which was set at PE3 and set the LP to 110
router bgp 65400
address-family vpnv4
neighbor "RR-IP" route-map community in
exit-address-family
route-map community permit 10
match community CUSTOMER
set local-preference 110
route-map community permit 20
ip community-list standard CUSTOMER permit 65400:1111
On PE2-- Under VPNv4 We match the community value 65400:2222 which was set at PE4 and set the LP to 110
router bgp 65400
address-family vpnv4
neighbor "RR-IP" route-map community in
exit-address-family
route-map community permit 10
match community CUSTOMER
set local-preference 110
route-map community permit 20
ip community-list standard CUSTOMER permit 65400:2222
Make Sure that RR is enabled to propogate the normal BGP communities as well...
Hope this helps to answer your question..Please let me know for any clarifications..
Regards
Varma

Load balance not happening in BGP

Dear Friends,
As per I know local BGP process may implement equal-cost load-balancing to the paths that:
Have the same set of path attributes up to the MED (weight, Local Preference, Origin, MED)
Are of the same type (both learned via iBGP or eBGP)
Have the same IGP cost to reach their NEXT_HOP IP address
If the above conditions are met andmaximum-paths [ibgp]is configured under the BGP process, BGP will install multiple equal-cost routes into the local RIB and use them for load-balancing. We call the above condition as load-balancing conditions for BGP.
As all the above criteria are matched still BGP is not doing load balance. Please find below routing table:
R1:
R1#sh ip bgp
BGP table version is 4, local router ID is 40.1.1.1
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
*>i192.168.1.0      20.1.1.2                 0    100      0 i
* i                        30.1.1.1                 0    100      0 i
R1#sh ip route
Gateway of last resort is not set
     20.0.0.0/24 is subnetted, 1 subnets
R       20.1.1.0 [120/1] via 10.1.1.2, 00:00:03, FastEthernet0/0
     40.0.0.0/24 is subnetted, 1 subnets
C       40.1.1.0 is directly connected, FastEthernet0/1
     10.0.0.0/24 is subnetted, 1 subnets
C       10.1.1.0 is directly connected, FastEthernet0/0
B    192.168.1.0/24 [200/0] via 20.1.1.2, 00:12:01
     30.0.0.0/24 is subnetted, 1 subnets
R       30.1.1.0 [120/1] via 40.1.1.2, 00:00:15, FastEthernet0/1
router bgp 100
no synchronization
bgp log-neighbor-changes
neighbor 10.1.1.2 remote-as 100
neighbor 40.1.1.2 remote-as 100
maximum-paths 2
no auto-summary
Please help....!!!!!!!   why BGP is not load balancing here????
R1#traceroute 192.168.1.1
Type escape sequence to abort.
Tracing the route to 192.168.1.1
1 10.1.1.2 88 msec 60 msec 28 msec
2 20.1.1.2 104 msec 56 msec 120 msec
Regards,
Sanjib

Dear Jon,
Thank you so much.
When I changed the configuration BGP is now loadbalancing. But in configuartion Max-path showing as 1 instead of 2.
R1#sh ip pro | sec bgp
Routing Protocol is "bgp 100"
Outgoing update filter list for all interfaces is not set
Incoming update filter list for all interfaces is not set
IGP synchronization is disabled
Automatic route summarization is disabled
Neighbor(s):
    Address          FiltIn FiltOut DistIn DistOut Weight RouteMap
    12.1.1.2
    13.1.1.3
Maximum path: 1
Routing Information Sources:
    Gateway         Distance      Last Update
    13.1.1.3             200      00:01:12
    12.1.1.2             200      00:02:15
Distance: external 20 internal 200 local 200
Regards,
Sanjib

Question about network statement in OSPF and BGP

The network statements in OSPF and BGP can be used to advertise networks. But I'm not clear under what circumstances would make more sense to use network statements to advertise a network than by using other methods to have the network learned by other routers.
Here is an example: assume I'm running BGP on router A. I want to advertise network 10.1.1.0/24 to other BGP peers. I have a OSPF route for this network. I can do 2 things: one is to use "network 10.1.1.0 mask 255.255.255.0", the other is to do "redistribute OSPF ... route-map OSPF-INTO-BGP", and create a prefix list to permit 10.1.1.0/24.
Both would work to have this network learned by other BGP peers. But which is better for what purpose?
Thanks a lot
Gary

Hi Gary,
There is one little difference between the use of the two approaches - the route injected into BGP by using a network statement will carry an Origin attribute of IGP, whereas the route injected using redistribution will have an Origin attribute of Incomplete. Now, that is not a huge issue since you can always change that whatever value you desire both with the use of the network statement and redistribution. The important thing, however, is that in the BGP best path selection process, the Origin attribute comparison is fairly high up and will prefer a route with the attribute of IGP.
Apart from that, there is absolutely no difference between using the network statement and using redistribution with a route-map that matches exactly on the same route that you would have specified with the network statement.
I guess one advantage of using the redistribute approach is that it does not clutter up the BGP config. If you wish to add more routes, you simply add them to the prefix list so that you don't really touch the BGP config portion at all..
Hope that helps - pls do remember to rate posts that help.
Paresh

EIGRP vs BGP route path selection scenario

I am looking for a routing solution to the following scenario. It is a fairly simple design.
I have two WAN connections between sites A and B. One is a 20 Meg Metro Ethernet Circuit running EIGRP. The other is a 10 Meg MPLS running BGP. What do I need to do in my configuration to make sure that the 20 Meg connection is the chosen path based off the fact that it has better speed and bandwidth? It appears to me that the MPLS is the preferred path even though it is slower.
See attached Diagram:
Site A Config
interface GigabitEthernet1/0/12
description PADC COX P2P 20 Meg
no switchport
bandwidth 20480
ip address 172.20.1.1 255.255.255.252
interface GigabitEthernet2/0/2
description LEVEL 3 MPLS
no switchport
bandwidth 10240
ip address 172.22.0.2 255.255.255.252
router eigrp 1
network 10.0.1.0 0.0.0.255
network 172.20.1.0 0.0.0.3
network 192.168.76.8 0.0.0.3
redistribute bgp 65003 metric 100 1 255 1 1500 route-map MPLS_NETWORKS
redistribute static route-map DEFAULT_ROUTE
router bgp 65003
bgp log-neighbor-changes
redistribute static
redistribute eigrp 1
neighbor 172.22.0.1 remote-as 1
default-information originate
Site B Config
interface GigabitEthernet0/1
description COX Communications 10 Meg to Venyu
bandwidth 20480
ip address 172.20.1.2 255.255.255.252
duplex auto
speed auto
service-policy output VOIP
interface GigabitEthernet0/2
description Level 3 MPLS
bandwidth 10240
ip address 172.22.1.2 255.255.255.252
duplex full
speed 100
router eigrp 1
network 10.3.1.0 0.0.0.31
network 10.52.1.0 0.0.0.255
network 10.76.6.0 0.0.0.255
network 172.20.1.0 0.0.0.3
network 192.168.63.64 0.0.0.63
network 192.168.76.249 0.0.0.0
passive-interface default
no passive-interface GigabitEthernet0/0
no passive-interface GigabitEthernet0/1
router bgp 65003
bgp log-neighbor-changes
network 10.3.1.0 mask 255.255.255.224
network 10.52.1.0 mask 255.255.255.0
network 10.76.6.0 mask 255.255.255.0
network 192.168.76.249 mask 255.255.255.255
neighbor 172.22.1.1 remote-as 1

If each router is receiving advertisements for the same networks/subnet masks from both BGP and EIGRP it will always choose the BGP routes because they have a lower AD ie. 20 vs EIGRP 90.
Doesn't matter what the bandwidth is.
If you want to prefer the 20Mbps links then there are a number of options -
1) if you can summarise each sites subnets then advertise the summary via BGP and the more specific via EIGRP. More specific will be chosen even before AD is taken into account.
2) change the AD of either BGP or EIGRP so EIGRP ends up with the lower AD
3) run BGP on both links although you would still need to manipulate the attributes to make sure the link you want is used.
Jon

BGP route selection from LAN to WAN

Hi,
I am going to implement a multihome internet connection to two different ISP. Before implementing in real network, I have prepared the same in GNS3 and testing. Subnet 10.x.5.0/24 should take R1 to outside from LAN and 10.x.6.0/24 should take R2 to outside from LAN.
Below is my configuration;
HSRP between R1 and R2 towards LAN. R1 is the primary HSRP device.
R6 is the host (example) and subnet .5.0/24 and .6.0/24 are connected to R6.
R6 is sending a default route to HSRP VIP.
R1 is advertising subnet 10.x.5.0/24 and R2 is advertising subnet 10.x.6.0/24
iBGP is configured between R1 and R2
From Internet to LAN:
From router 5 (exam.: Internet) traffic is divided in to two routers. traffic for 10.x.5.0/24 coming to R1 and traffic for 10.x.6.0/24 coming to R2. This is absolutely fine. What i expected.
From LAN to Internet:
I need traffic from 10.x.5.0/24 should take R1 to go to internet (outside) and from 10.x.6.0/24 should take R2 to go to Inernet (outside).
I have tried with higher Local Preference on each router but is not working. All traffic from R6 (i.e. LAN) to outside is taking only R1 to go outisde.
Could any one can help on how I can share traffic for 10.x.5.0/24 & 10.x.6.0/24 divided in two Routers from LAN.
Diagram is attached.

As answered in other post, hosts belong to LAN2 (subnet 10.x.6.0/24) can have default gateway set to R2 (R2 could be HSRP active node) now R2 will have route from eBGP (AS300) as well ibgp session (from R1). We can tweak BGP attribute to prefer eBGP session. One good option is to set weight as we want to prefer AS300 routes locally to the router and not on R1. Similarly on R1 put weight for AS200 routes.
Regards,
Akash

BGP decision algorithm - help needed - stumped

Hello gurus! hoping for a BGP expert to chime in here. Im studying for my CCIE, and there is something in Jeff Doyle's Routing TCP/IP vol2 book that I just cant seem to figure out and its really stalling my understanding of the BGP path selection algorithm.
Its on pg 195, example 3-57, attached as an image in this post (Ive also attached the network diagram that this output refers to). Basically its an output of "show ip bgp" and whats stumping me is simply: for the aggregate route 192.168.192.0/21, why has this router selected as best (>) the one via next hop 192.168.1.254?? I would have thought based on the presence of the LocalPref = 100 on the 192.168.1.237 route that would have been selected. But apparently not! Heres a walk through of the path selection logic as i understand it:
1/WEIGHT: both 0, so skipped.
2/LOCAL_PREF: this is my problem, .237 should win, but ignoring for now...
3/ORIGINATED LOCALLY: neither are they are learnt from BGP peers, so skipping.
4/AS_PATH: both identical, AS100 only, so skipping
5/ORIGIN CODE: both are 'i' (IGP), both were created from "aggregate-address" statements on their originating routers downstream in AS100
6/MED: both empty, so skipping
7/PREFER [eBGP] over [confedBGP] over iBGP: so the .254 route apparently wins on this condition... which in isolation, i agree with (clearly the eBGP .254 route is better than the .237 iBGP candidate).
.... however what about step 2/LOCAL_PREF!?
looking forward to some expert guidance here to help me squash this one :)
thank in advance,
Keiran

Hello,
Keiran are you talking about "Orgin" attribute or ORIGINATED LOCALLY as this attribute i am not able to find it...that attribute anywhere:
http://netcerts.net/bgp-path-attributes-and-the-decision-process/
Path Attributes:
Attribute
Class
ORIGIN
Well-know mandatory
AS_PATH
Well-know mandatory
NEXT_HOP
Well-know mandatory
LOCAL_PREF
Well-know discretionary
ATOMIC_AGGREGATE
Well-know discretionary
AGGREGATOR
Optional transitive
COMMUNITY
Optional transitive
MULTI_EXIT_DISC (MED)
Optional nontransitive
ORGINATOR_ID
Optional nontransitive
ORGINATOR_ID
Optional nontransitive
CLUSTER_LIST
Optional nontransitive
Also there is similar question on learning forums:
https://learningnetwork.cisco.com/thread/36845
From the forum:
"Locally Originated means that the local router is the one that generated the route with either a network statement, and aggregate statement, redistribution, or conditional route injection. It's not an attribute that is included in the UPDATE messge, instead it's just used by the local process as part of the path selection, where the router will prefer its own locally originated routes over someone else's origination of the same prefix."
Hopefully this will help.
BTW i am reading same book and too bad Mr. Doyle did not include full configs for all routers, as i am trying to simulate his scenarios sometimes it is not working as in his book, now i have issue on next page 197 why Orgin IGP is not taking precedence over Incomplete even if one is learned via EBGP and other over iBGP...driving me nuts.
Regards,
Lukasz

BGP Community additive out of order?

From cli output:
13237 3356 3549 22047
    195.69.144.212 from 195.69.144.212 (82.197.128.1)
      Origin IGP, localpref 100, valid, external
      Community: 3356:2 3356:22 3356:86 3356:501 3356:666 3356:2065 3549:4852 3549:34152 13237:44049 13237:46067
      Last update: Fri Apr 30 06:28:19 2010
the community items sequence doesn't match the as-path( 3356 - 3549 - 13237 vs. 13237 3356 3549... )
if they are using additive community features, what would cause this?
TIA.

Hello Gviewer,
in example 3-141 of TCP/IP vol.II is shown a sh ip bgp from a router internal to AS 100 named colorado.
AS path attribute is 2000 because AS 100 is not added to AS path in an iBGP session within AS 100 (it will be added when sending the update to another AS)
so community 2000:xx is set by eBGP peer (austria) and later BGP community 100:yy is set by iBGP peer (Idaho) of the router in which the sh ip bgp is been performed (colorado)
to be noted the eBGP peer of the router of example 3-141 will see an AS path of 100 2000 with BGP community 100:yy 2000:xx and this would be more similar to what you have seen in your tests.
The key point is that 100:xx is added by an iBGP peer.
Hope to help
Giuseppe

BGP received-only Question

Hi
From what I understand in the show ip bgp x.x.x.x/x output the received-only would be present when soft-reconfiguration inbound is configured and the route has been rejected by a policy i.e. a route map
What i have also found is that on many outputs i can see the exact same route in the output twice, one which has the received-only keyword and one doesn't.
Now for a specified neighbor we have a route map configured inbound which will change the weight based on the community value. It seems as though when a route map is configured and an attribute is changed that route appears in the output twice, one being modified and one which is unchanged. But this contradicts what is said on the Cisco website its states 'the received-only keyword will only show up if the route is denied by a policy', but its not.. it's just changed.
Has anyone had this discussion before? I would like to hear people's thoughts on the matter.
Thanks
Andre
corerouter#show ip bgp | b 10.141.54.0
* 10.141.54.0/23 10.199.10.18 0 64000 34406 65502 ?
*> 10.199.10.18 0 64000 34406 65502 ?
corerouter#sho ip bgp 10.141.54.0/23
BGP routing table entry for 10.141.54.0/23, version 1219279
Paths: (4 available, best #3, table Default-IP-Routing-Table)
Advertised to update-groups:
2 3 4 5 6 7
34406 65502
10.199.10.18 from 10.199.10.20 (82.196.60.60)
Origin incomplete, metric 0, localpref 100, weight 64000, valid, external
Community: 10199111
34406 65502, (received-only)
10.199.10.18 from 10.199.10.20 (82.196.60.60)
Origin incomplete, metric 0, localpref 100, valid, external
Community: 10199111
34406 65502
10.199.10.18 from 10.199.10.19 (82.196.60.1)
Origin incomplete, metric 0, localpref 100, weight 64000, valid, external, best
Community: 10199111
34406 65502, (received-only)
10.199.10.18 from 10.199.10.19 (82.196.60.1)
Origin incomplete, metric 0, localpref 100, valid, external
Community: 10199111

show ip bgp neighbor x.x.x.x received-routes
show ip bgp neighbor x.x.x.x routes
sho ip bgp a.b.c.d
If you found this page, like I did, while searching for "received-only" - that means that the route has only been received, but not entered in the routing table. This is good if you meant to block that route. But if that route is actually also installed in the routing table and you meant to block it, check your route-map, specifically your prefix-lists and you will likely find that you have an error with wither the IP address or the CIDR mask, resulting in a non-match condition. The inverse is also true if you intend to allow a route but you only see the "received-only" route, you probably have a typo in your route-map or prefix list. Below are some examples that might help.
Here are some BGP with route-map and prefix-list examples, although the data is not meaningful.
router bgp 1234
neighbor CARRIER1 peer-group
neighbor CARRIER1 route-map PROVIDER1-IN in
neighbor 6.7.8.9 peer group CARRIER1
route-map PROVIDER1-IN deny 5
match ip address prefix-list MyIPs
route-map PROVIDER1-IN permit 10
match ip address prefix-list GOOG APPL
ip prefix-list GOOG seq 5 permit 8.8.8.0/24 le 32
ip prefix-list GOOG seq 10 permit 8.8.4.4/32
ip prefix-list APPL seq 5 per 17.142.160.59/32
ip prefix-list APPL seq 10 per 17.178.96.0/24 le 32
ip prefix-list MyIPs seq 5 per 1.2.0.0/16 le 24
ip prefix-list MyIPs seq 10 per 2.3.4.0/24 le 32
ip prefix-list MyIPs seq 15 per 4.5.6.7/32

BGP Multihoming

Hi
I would like to do a BGP multihoming with our service providers for our internet connection
and will to advertise the following networks 213.13.222.0/27 and 213.13.222.32/27 to both ISP
I want to distribute my traffic to both the ISP without getting the entire routing table from the ISPs
The internet browsing traffic needs to be forwarded to ISP B and the other static NAts to be forwarded to ISPA with each ISP acting as fallback to each other. THis will be achieved by policy routing wherein the browsing traffic will natted from the range 213.13.222.0/27 and the others will be natted from the range 213.13.222.32/27.
Now heres what i feel i would have problem
Can i have specific attributes applied to only a set of routes advertised to one BGP neighbor. Heres the config i plan
Router bgp 31380
Network 213.13.222.0 mask 255.255.255.227
Network 213.13.222.32 mask 255.255.255.227
Neighbor 111.111.111.111 remote-as 200
Neighbor 111.111.111.111 route-map ISPA-local-routes out
Neighbor 111.111.111.111 route-map Acceptroutes in
Neighbor 123.123.123.123 remote-as 300
Neighbor 123.123.123.123 route-map ISPB-local-routes out
Neighbor 123.123.123.123 prefix-list Acceptroutes in
access-list 1 permit 213.13.222.32 0.0.0.31
access-list 2 permit 213.13.222.0 0.0.0.31
access-list 3 permit 0.0.0.0
ip prefix-list? Acceptroutes seq 5 permit 0.0.0.0/0
Route-map ISPA-local-routes permit 10
Match ip address 1
Set as-path prepend 31380 31380 31380 31380 31380
Route-map ISPA-local-routes permit 20
Match ip address 2
Route-map ISPB-local-routes permit 10
Match ip address 2
Set as-path prepend 31380 31380 31380 31380 31380
Route-map ISPB-local-routes permit 20
Match ip address 1
Set as-path prepend 31380 31380 31380 31380 31380
route-map browsing-traffic permit 10
match ip address 1
set ip next-hop 111.111.111.111
interface fastethernet 0/1
ip address 159.145.145.1
ip policy route-map browsing-traffic
Will the above config work for my scenario. Also i need to know whether the return trafiic for browsing will be from ISPB and not from ISPA
Thanks in Advance
Narayan

Narayan:
A few issues:
1. Route-map ISPB-local-routes permit 10
Match ip address 2
Set as-path prepend 31380 31380 31380 31380 31380
Route-map ISPB-local-routes permit 20
Match ip address 1
Set as-path prepend 31380 31380 31380 31380 31380
I'm guessing you wanted to do:
Route-map ISPB-local-routes permit 20
Match ip address 1
2. route-map Acceptroutes needs to use access-list 3 or ip prefix-list Acceptroutes to have the default route in:
route-map Acceptroutes permit 10
match ip address 3 or Acceptroutes
3. route-map browsing-traffic permit 10
match ip address 1
set ip next-hop 111.111.111.111
interface fastethernet 0/1
ip address 159.145.145.1
ip policy route-map browsing-traffic
I guess FE0/1 is your inside interface. With your config, route-map browsing-traffic will be applied before natting. So the address to match is not your natted address but the private addresses before they are natted.
I think a better way to achieve what you want is to use nat pool and dynamic natting with route-map, which would be configured that if your traffic outbound is HTTP and/or HTTPS for web browsing, nat it to one /27 and set the next hop to the ISP desired, for everything else outbound, send it to the other ISP as next hop.
4. This should be just part of your config. Make sure other config is in sync with this part.
Let me know what you think.
Gary

Monitoring a BGP route and AS-PATH.

Hello.
I need to receive a SNMP trap when a BGP route, received with a specific AS-PATH, disappears from routing table.
Any ideas?
Thanks.
Andrea

You can use EEM for this. Check out the cisco beyond web site for sample scripts that may help you do this.
A company that I used to work for, www.magnus.net had a mature EEM solution for doing this for large network environments. They took a standalone router and using EEM turned it into a route monitor. It would send out notifications when BGP routes of defined attributes like AS-Path diasappeared from routing tables. It was driven by an excel spreadsheet as inputs. It was written by a super CCIE engineer.

BGP attributes V/S BGP Comunity

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