Bgp path selection issue

hi,
i have the following cli show command output,
R2#show bgp ipv4 unicast
BGP table version is 11, local router ID is 192.168.220.252
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
* i192.168.30.0     192.168.110.70           0    100      0 63000 i
*>                  192.168.220.70           0             0 63000 63000 i
* i192.168.40.0     192.168.110.70           0    100      0 63000 63000 i
*>                  192.168.220.70           0             0 63000 i
R2#
why isn't the route through the shortest AS path not selected as the best route for 192.168.30.0. ?
thanks,
uddika

R2#
R2#
R2#show ip bgp 192.168.30.0
BGP routing table entry for 192.168.30.0/24, version 7
Paths: (2 available, best #2, table Default-IP-Routing-Table)
Advertised to update-groups:
     2
63000
    192.168.110.70 (inaccessible) from 192.168.111.251 (192.168.111.251)
      Origin IGP, metric 0, localpref 100, valid, internal
63000 63000, (received & used)
    192.168.220.70 from 192.168.220.70 (192.168.220.70)
      Origin IGP, metric 0, localpref 100, valid, external, best
R2#
R2#
thanks, i noticed that R2 does not have the route for the next hop, 192.168.110.70.

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Weird BGP path selection problem

Hi, all,
I am seeing a weird BGP path selection problem on 4948 switch running cat4500-entservicesk9-mz.122-46.SG.bin code, this switch has two uplinks to the same ISP's different edge router, one circuit is primary the other one is strict backup, only default route is accepted from ISP. I am setting both local preference and weight to the default route advertised over backup link, however neither one is taking effect, BGP still thinks the backup link is better, what could be wrong?
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Thanks

Hi,
On cisco routers , weight is having highest preference to decide best path. By default for received route, weight is 0 but you are setting weight 90 to backup path and that is why it is getting preferred (higher is better). Please remove weight and let local preference be 90 (lesser than route on primary path)
--Pls dont forget to rate helpful posts--
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Akash

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I've been poking around in a few test routers trying to find where BGP states how long a route has been known from a neighbor. Based on Cisco's BGP path selection article: http://www.cisco.com/c/en/us/support/docs/ip/border-gateway-protocol-bgp/13753-25.html, #10 states BGP prefers the oldest known route.
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With reference to cisco's document on BGP Best Path Selection Algorithm (http://www.cisco.com/c/en/us/support/docs/ip/border-gateway-protocol-bgp/13753-25.html).
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Can anyone explains here, as this document has not considered the AS-PATH during path selection and used lowest ROUTER ID only.
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Hey Buddy
The AS_PATH for both is only 1, don't get confused by (AS_SET) which only counts as 1 no matter how many AS are in the set. Refer to section "How the Best Path Algorithm Works"
4.Prefer the path with the shortest AS_PATH.
Note: Be aware of these items:
◦An AS_SET counts as 1, no matter how many ASs are in the set.
So bearing the above in mind
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Path6
(64955 65003) 65089 --- this equals 1
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      Extended Community: RT:1100:1001
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!--- BGP selects this as the Best Path on comparing
!--- with all the other routes and selected based on lower router ID.
Path8
(65003) 65089 --- this equals 1
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      Extended Community: RT:1100:1001
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Both paths have reachable next hops
Both paths have a WEIGHT of 0
Both paths have a LOCAL_PREF of 100
Both paths are learned
Both paths have AS_PATH length 1 --- because the (AS_SET) always equals 1
Both paths are of origin IGP
Both paths have the same neighbor AS, 65089, so comparing MED.
Both paths have a MED of 0
Both paths are confed-external
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Hope it helps (:

Path Selection issue in Table Test

Hi All
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Hi Deepu,
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Path selection issue

Hi All
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Appreciate your feed back.
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Hi Deepu,
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BGP Best Path Selection Algorithm

How is the administrative distance positioned in the bgp route decision ?
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the path learned from eBGP or the path with higer local prefernce ?

For your scenario the path with the higher local pref will be installed in the routing table althogh its ibgp.
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the router will compare them with the bgp path selection algorithm
the one that wins will be installed in the routing table with the admin distance of the kind of route it is so if the ibgp route won the path selection you will see in the routing table the admin distance of 200,if the ebgp route won you'll see 20 in the admin distance.
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After reading up on some of the problems people are having with the path/shape changes in CC 2014, I haven't seen an exact mention of the problem I am having so here I am.
2 part problem really:
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When working on a shape, pressing return will turn the outline on and off as expected. Pressing esc will turn it off as expected, double clicking will take it into isolation mode as expected but then sometimes, the whole outline becomes unresponsive and it isn't visible. The shape layer is selected and the layer selection changes as expected when I have All Layers mode on and I click different shapes. The path is also selected in the Path panel. It shows up in the properties window too. Clicking/double clicking the shape, return and esc make no difference. I don't get it its all happening randomly though
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Specific path selection in E-BGP

I have two routers ASR 9K platform with the image file is "disk0:asr9k-os-mbi-4.3.4.sp4-1.0.0/0x100305/mbiasr9k-rsp3.vm"
Primary link b/w Router 1 and 2 :
Router 1 ------> Directly connected with 30G to Router 2 on a bundle ( Neither ISIS nor BGP running on this link )
Router 2 ------> Directly connected with 30G to Router 1 on a bundle ( Neither ISIS nor BGP running on this link )
Secondary link b/w Router 1 and 2 :
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Sankar.

Hi,
The OSPF traffic would not pass through the VSL link. The path would directly go from each 4500 to the 3945 (Equal cost load balancing). I think, the 3900 series supports Etherchannel, if this is the case you can also create a L-3 Portchannel between the VSS and 3945 router. This way you use one /30 instead of 2 and you still have redundancy. For BGP, I would do one peering with Loopbacks.
HTH

Inject BGP Default Routes into Multiple VRF before Best Path Selection

Hello,
I have the following setup:
Multiple Border Routers with eBGP sessions to external AS. We receive a default route from this multiple AS to keep the Table manageable. We noticed an important part of our traffic was been SW routed instead of CEF when we had the Full Internet table. Router Resources came to the ground when we changed to a default.
Now I want to separate this default routes into different VRF. Attached is the Diagram.
My question is, the multiple default route all go into the BGP Table. The BGP table then select the best route and place it on the RIB and then to the FIB.
I want to redistribute the different Route on the BGP table prior to the Best path selection algorithm and placed on the RIB.
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Hi,
Redistribution of multiple routes to same prefix is not possible. Even if you have configured BGP multipath and all different bgp routes got installed into routing table, during redistribution only route will be redistributed.
Also would like to understand the requirement of redistributing multiple BGP routes in to IGP. As per your diagram, 3 different eBGP sessions are on three different routers, so you can prefer eBGP route over iBGP received from other routers and can distribute eBGP route to IGP from each router. Thus you will have three different default routes in to IGP in core.
Please don't forget to rate this post if it has been helpful
- Akash

Path Selection between 10 gig fiber and microwave

Hello everyone,
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since ospf metric is cost ( or bandwidth ), the 10 gig ethernet connection is always preferred. however, sometimes the 10 gig link is flapping or the bit error rate is bad, is there anyway to change the path selection to go through the microwave when the bit error rate in the 10 gig link is bad or the link flaps ?
basically can we make the path selection based on anything than the speed or cost ?

Disclaimer
The Author of this posting offers the information contained within this posting without consideration and with the reader's understanding that there's no implied or expressed suitability or fitness for any purpose. Information provided is for informational purposes only and should not be construed as rendering professional advice of any kind. Usage of this posting's information is solely at reader's own risk.
Liability Disclaimer
In no event shall Author be liable for any damages whatsoever (including, without limitation, damages for loss of use, data or profit) arising out of the use or inability to use the posting's information even if Author has been advised of the possibility of such damage.
Posting
Bandwidth can be a metric to OER/PfR. Much else can be used by OER/PfR.
The intent of this technology is sort of described by the names, Optimized Edge Routing (v1) and Performance Routing (v2).
Both can account for path bandwidth and/or analyze performance.
Understand typical dynamic routing protocols keep track of paths between source and destination and some have a way to "weight" paths (for example, OSPF link cost [which by RFC, hasn't nothing to do with bandwidth, but is often based on that]).
OER/PfR, for example, can run their own SLA tests.
Years ago, I set up OER in large dual MPLS/VPN environment. Our initial "problem", after activation, our WAN performance monitoring tools (and our users!) no longer "saw" any WAN performance issues. They were still happening, but OER "saw" them first, and worked around them before the monitoring tools saw them.

DMVPN + MPLS best-path selection

Dear Community
We're in the process of deploying DMVPN as a backup solution to MPLS. All that is working great!
The DMVPN wan is dual-cloud, with 2 hub routers in each cloud. Phase 3 (nhrp shortcut) is enabled on all the spokes.
For routing, all the customer subnets are advertised in MPLS, whereas for DMVPN hub advertises only a summary to 10.0.0.0/8. The protocol for both is BGP. For DMVPN, the hub routers resides in one AS (65002) and all the spokes another common AS 65102. DMVPN is therefore peered eBGP hub > spoke.
For customers connected to MPLS, the DMVPN serves as backup only solution. Best-path selection by longest prefix match.
We have other customers coming on board who wish to join the same WAN but don't have the $$$ for MPLS so are opting for DMVPN only.
Now, I have a requirement to enable spoke-to-spoke for a DMVPN only site (spokeA) to an MPLS site (spokeB). The problem is it doesn't seem to work properly as the hub router sees the best path to spokeB site via MPLS, not via DMVPN. The spoke-to-spoke is never formed, and remains spokeA > hub > mpls > spokeB. The return path is better = spokeB > DMVPN > hub > spokeA (this is because spokeB sees no route from MPLS for spokeA, so follows 10.0.0.0/8) route.
I look for any feedback that can help to meet this requirement?
And if any advice on the general design would be really appreciated.
Thanks a lot!
Phil

Phil,
I did a short lab around this ... wanted to make sure I'm not saying something stupid.
While I can't claim it's the _optimal_ solution for your setup it seems to work in my lab.
Spoke1 LAN 192.168.101.0/24 (AS 65001)
Spoke2 LAN 192.168.102.0/24 (AS 65002)
HUB LAN 192.168.111.0/24 (AS 65000)
192.168.1.0/24 DMVPN subnet.
A single (i)VRF - DMVPN exists on hub, only and is assigned only to DMVPN tunnel interface.
Excuse a few hacks a had to use... default routed via default-originate for example :-)
Hub
R10-P#sh run int tu0
Building configuration...
Current configuration : 281 bytes
interface Tunnel0
vrf forwarding DMVPN
ip address 192.168.1.1 255.255.255.0
no ip redirects
ip nhrp map multicast dynamic
ip nhrp network-id 1
ip nhrp shortcut
ip nhrp redirect
tunnel source Loopback0
tunnel mode gre multipoint
tunnel protection ipsec profile PRO
end
R10-P#sh run | s r b
router bgp 65000
bgp log-neighbor-changes
network 192.168.111.0
redistribute static
neighbor 10.112.112.1 remote-as 65001
neighbor 10.112.112.1 route-map SPOKES_MPLS in
default-information originate
address-family ipv4 vrf DMVPN
neighbor 192.168.1.101 remote-as 65001
neighbor 192.168.1.101 activate
neighbor 192.168.1.102 remote-as 65002
neighbor 192.168.1.102 activate
exit-address-family
R10-P#sh run | s vrf defini
vrf definition DMVPN
rd 1:1
route-target export 100:1
route-target import 100:1
address-family ipv4
import ipv4 unicast map DEFAULT
export ipv4 unicast map SPOKE_SUBNETS
route-target export 100:1
route-target import 100:1
exit-address-family
address-family ipv6
route-target export 100:1
route-target import 100:1
exit-address-family
Result on spoke
R1-PE#traceroute 192.168.102.1 source e2/0
Type escape sequence to abort.
Tracing the route to 192.168.102.1
VRF info: (vrf in name/id, vrf out name/id)
1 192.168.1.1 [AS 65000] 5 msec 10 msec 2 msec
2 192.168.1.102 [AS 65000] 4 msec * 5 msec
R1-PE#traceroute 192.168.102.1 source e2/0
Type escape sequence to abort.
Tracing the route to 192.168.102.1
VRF info: (vrf in name/id, vrf out name/id)
1 192.168.1.102 [AS 65000] 6 msec * 6 msec
routing on hub
(sanitized)
R10-P# sho ip route
Gateway of last resort is 10.100.100.2 to network 0.0.0.0
S* 0.0.0.0/0 [1/0] via 10.100.100.2
10.0.0.0/8 is variably subnetted, 13 subnets, 2 masks
B 192.168.101.0/24 [20/0] via 10.112.112.1, 00:06:40
B 192.168.102.0/24 [20/0] via 192.168.1.102 (DMVPN), 00:00:03
192.168.111.0/24 is variably subnetted, 2 subnets, 2 masks
R10-P# sho ip route vrf DMVPN
Routing Table: DMVPN
Gateway of last resort is 10.100.100.2 to network 0.0.0.0
B* 0.0.0.0/0 [20/0] via 10.100.100.2, 00:06:40
192.168.1.0/24 is variably subnetted, 2 subnets, 2 masks
C 192.168.1.0/24 is directly connected, Tunnel0
L 192.168.1.1/32 is directly connected, Tunnel0
B 192.168.101.0/24 [20/0] via 192.168.1.101, 00:06:40
B 192.168.102.0/24 [20/0] via 192.168.1.102, 00:06:25

OSPF Equal Cost Path Selection

This is a nerdy enough qeury in reality.
We have a single area - area 0.0.0.32. All intra-area routes. We have 2 switches in the core of the network, and 10 switches at the edge. All of these switches are connected via layer 3 OSPF routed links.
The cost for all links is 20 - which is based on bandwidth between the boxes - which is 2Gbps.
Have a look at the enclosed jpeg to get an idea.
Very simple.
Query revolves around the path selection available to OSPF.
The path from Core 2 to the 10.32.51.0 network is easy - straight across the link between the core switches for a cost of 20.
Question :- if the link between the cores fail, which path will be chosen by OSPF and why?
It can go through ANY of the other edge switches for a total cost of 40, but it will choose a particular one. What criteria does OSPF use to select this path?
Remember, the path costs are equal, they are all intra-area.
I tried messing with Router ID, but this doesn't seem to be it.
I tried highest interface IP addresses, but it doesn't seem to be this.
It is not a random act, the algorithm chooses the same one every time.
There must be some parameter in the LSDB that is the defining one when it comes to path selection.
Can you help me out please. I need someone who understands the OSPF algorithm better than I do (which might not be hard!).
Appreciate any comments for debate.

Disclaimer
The Author of this posting offers the information contained within this posting without consideration and with the reader's understanding that there's no implied or expressed suitability or fitness for any purpose. Information provided is for informational purposes only and should not be construed as rendering professional advice of any kind. Usage of this posting's information is solely at reader's own risk.
Liability Disclaimer
In no event shall Author be liable for any damages whatsoever (including, without limitation, damages for loss of use, data or profit) arising out of the use or inability to use the posting's information even if Author has been advised of the possibility of such damage.
Posting
My guess (as I haven't re-read the RFC), selection of an ECMP to retain in a routing table (assuming all possible ECMP are not retained) and/or exactly how packets or flows are ECMP routed is implementation dependent.
I recall years ago bumping into a situation where I had 6 (OSPF) ECMP on a Cisco router which had the (then) default allowance of 4 ECMP in the route table. I don't recall exactly what the issue was, but whatever it was doing I considered it a bug. The "fix" was to allow the router to use all 6 ECMP. (Again, don't remember the specifics, but the issue I saw was more involved than 2 of the 6 ECMPs weren't retained.)

BGB Best path selection

Hi,
Could someone tell me why second path remains as best?
MPLS_CORE#show ip bgp 192.168.1.0
BGP routing table entry for 192.168.1.0/24, version 27
Paths: (2 available, best #2, table default)
Advertised to update-groups:
1
Refresh Epoch 1
64513
2.2.2.1 from 2.2.2.1 (10.201.240.2)
Origin incomplete, metric 156160, localpref 100, valid, external
rx pathid: 0, tx pathid: 0
Refresh Epoch 1
64512
1.1.1.1 from 1.1.1.1 (192.168.4.253)
Origin incomplete, metric 1415680, localpref 100, valid, external, best
rx pathid: 0, tx pathid: 0x0
Regards
Michal

Hi Michal,
Please refer below CCO document for BGP best path selection criteria on cisco routers
http://www.cisco.com/c/en/us/support/docs/ip/border-gateway-protocol-bgp/13753-25.html
If everything attribute is same then it comes to router-id and lowest router-id is preferred.
11. Prefer the route that comes from the BGP router with the lowest router ID.
The router ID is the highest IP address on the router, with preference given to loopback addresses. Also, you can use the bgp router-id command to manually set the router ID.
In your case, second route is having lowest router-id (1.1.1.1)
--Pls dont forget to rate helpful posts--
Regards,
Akash

Path Selection – Leaving blank holes

Hello,
I'm missing a very important feature since I switched from CS4 to CS 5.5: In Photoshop CS4, when you created a path in another and selected the path, the inner path was left blank (Creating an "o" and selecting it got you the selection in shape of an o).
Now, as I'm using CS5.5, Photoshop totally ignores those inner pathes and makes one big selection (example: http://dl.dropbox.com/u/5024014/path.png). This is very bad for me, because I have to put big industrial machines on transparent background, and now I have to create dozends of paths for every litte hole and then must put them together manually, which takes a lot of time.
So, if anyone knows how to solve this problem and getting my path selection back to how it worked in CS4, I would be very glad!
Greetings, Andreas

Bgp path selection issue

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