A method of implementing a backup path in an autonomous system as for failure of an interas link is described. This behavior promotes path diversity and reduces multiexit discriminator med oscillations. The border gateway protocol bgp is the routing protocol of the internet, used to route traffic across the internet. An engineer is working to provide high availability to a service provider core network. Acx series,m series,mx series,t series,srx220,srx650,srx240,srx210,srx110,srx100,ptx series,qfx series,ex4600. Youre trying to create a backup path, but thats still the wrong command. Yang modules from standards organizations such as the ietf, the ieee, the metro ethernet forum, open source such as open daylight or vendor specific modules yangmodelsyang. Typically, bgp peers can only send a single path to eachother, with any updates for that path replacing the existing one. Advertise customer routes to all pe routers by configuring the ipv4 addressfamily under the mp bgp configuration mode. Configuring bgp additional paths for each address family. Bgp fast reroute is a feature that brings together indirection techniques in the forwarding plane and precomputation of bgp backup paths in the control plane to support fast reroute of bgp traffic around unreachablefailed bgp nexthops. On the internet, its more important that you have granular control over how you forward your traffic and to which autonomous systems instead of just going for the shortest path based on a metric.
Which bgp command enables a backup path to be installed in the rib and cef tables. If you know the enemy and know yourself, you need no fear the result of a hundred battles. Cisco 4g lte and cisco 4g lteadvanced network interface module software configuration guide. We have a route policy configured and this works for the backuppaths but we are still getting additional paths. Command reference manual, routing configuration manual, reference manual, configuration manuallines, configuration manual, user configuration manual, installation manual, service configuration manual, getting started manual, system configuration manual, software manual. On the other hand, the bgp additionalpaths install command triggers computation of a backup path or bestexternal path. I want almost the same thing but i want to make one link as primary and one as backup, if primary link goes down the backup should be use. Now i want to configure my primary circuit 2xe1 and have this used as my main route inout, and if it fails switch over to use the adsl backup. We have a backup link with the same isp, and i have been trying to find an example that i can use that shows the configuration required to send all traffic via the primary link unless there is a failure, at which time it will then send all traffic via the backup link until the primary link is. If the bgp additionalpaths select command is not configured, the bgp additionalpaths install command will trigger both computation and installation of a backup path as is done with the bgp pic feature. Im trying to get my windows 2012 server to establish a bgp session with a vendors router i assume cisco. May 18, 2015 in a non bgp multipath environment, this command installs backup paths in additional to the best one elected by bgp. Hi all, i have very little experience with bgp, and have so far configured up our primary isp link. Bgp border gateway protocol uses an attribute list for path selection.
Ccie service provider techtorial lizabete cacic technical leader ovidiu constantin senior system engineer 2. Antispam antispyware antivirus aspath asn as prepend autosummary bgp bgp asn bgp community string bgp configuration bgp default route bgp isp bgp neighbor cisco conditional bgp configuration controlling customers ebgp free full route howto hsrp ibgp intrusion detection isp loadbalancing loadsharing localpref maximum path metric multihop. With the bgp additional paths feature, bgp advertises multiple paths for the same prefix so we have path diversity instead of path hiding. This path will be selected as the best path in the bgp rib and will be the only path reflected to route reflector client r5. When the bgp pic feature is enabled, by default, bgp recursion host is configured for vpnv4 and vpnv6 address families and disabled for ipv4 and ipv6 address families. Addpath feature will send bestpath, nbestpath, n1bestpathetc. An important observation is that distribution of more than one best path by autonomous system border routers asbrs with multiple ebgp peers attached to it where no next hop self is set may result in bestpath selection inconsistency within the autonomous system. Remember not to use bgp additionalpaths select backup that command is for diversepath or for local nonadvertised selection of a backup route. The technologies behind the scenes are very complicated to practice, though the general understanding is easy to understand, which.
Such lack of path diversity can lead to med oscillations, prevents an efficient use of multipath bgp and does not allow for a fast and local recovery upon nexthop failure. Bgp backup with static routes bgp cisco certified expert. Bgp convergence could be seconds or minutes that would cause packet loss. Advertising multiple paths in bgp bgpaddpath noction. The bgp best external feature will not install a backup path if bgp multipath is installed and a multipath exists in the bgp table. The path id is similar to how the rd route distinguisher works in mpls vpn, except the path ids can be used in any. The backup alternate path provides a fast reroute mechanism to counter a singular network failure. Bgp supports ecmp equal cost multipath routing but by default, it only uses a single path. Configure route targets that are used for importing and exporting customer vrf routes e. Is it possible to have a default drop so only the specific backup routes get added. Ios xr bgp additional path issue the it networking community.
Us7852772b2 method of implementing a backup path in an. It will still select one path as the best path via the final four tie breakers oldest bgp path, lowest router id, shortest cluster list, or lowest bgp neighbor id. The second best path is called the backupalternate path. The bgp table on service provider backup router contains the floating static route. Bgp installs the best and backupalternate paths for the prefixes into the bgp rib. To locate documentation for other commands that might appear while performing a configuration task, search online in the cisco asr 9000 series router software master command index.
This is called bgp multipath and it must be explicitly enabled using the multipath command. Internetdraft diverse bgp pathdist july 2012 this new requirement comes with its own memory and processing cost. For those prefixes, bgp calculates an additional secondary best path along with the primary best path. For that reason, its a pretty important protocol, and it can also be the hardest one to understand.
For more information about bgp and complete descriptions of the bgp commands listed in this module, see related documents section of this module. Cisco ios supports load balancing for ebgp and ibgp. Configures the system to calculate a best external path external to rr cluster. Internetdraft draftietfidradd paths guidelines08 apr 2016 1. Good for host potato routing, no need for full mesh, but could use rr. Routing information received via the bgp protocol often contains more than one route to the same destination. So the current total number of pes dedicated for vpn functionality is around 400 2 pes in each pop x 200. May 19, 2016 cisco public 60 ce1 ce8 pe2 pe3 rr4 rr5 pe6 pe7 bgp addpath configuration routepolicy rp set pathselection backup 1 advertise install.
Bgp fast reroute is supported with ipv4, labeledipv4, ipv6, 6pe, vpnipv4 and vpnipv6 routes. This extension helps reduce route oscillations rfc3345 and achieve faster reconvergence, as an alternative path is immediately available when a primary path fails. Ios xr bgp additional path issue ieoc the it networking. Ip routing configuration guide, cisco ios xe amsterdam 17. The second best path is called the backup alternate path. Bgp however, selects the best path based on a list of attributes. The advantage that bgp has over all other routing protocols is the ability to control path selection based on different routing policies. The rfc7911 discusses a bgp extension that allows the advertisement of multiple paths addpath for the same prefix nlri. The second path is seen as the backup correctly, but doesnt get advertised to anyone. With the addpath receive configuration, router r4 is configured to receive multiple paths from router r1. I think if it asks for both r15 and 16,using seperate rd will do the trick.
If the best path can be installed in the route table and there are other bgp paths locrib routes for the same ipv4 or ipv6 prefix that are nearly as good as the best path the additional paths can also be installed in the route table. By increasing the routerlevel bgp diversity within an as, add paths reduces the likelihood of propagation of bursts of bgp withdraw and update messages outside the as for a. Cisco content hub cisco 4000 series integrated services routers. Us20070091796a1 method of implementing a backup path in an. The policy to apply to influence traffic into and out of your network should be based on what fits within your existing deployment and what you find easiest to manage.
Guaranteeing bgp stability with a few extra paths request pdf. This convergence is applicable to both core and edge failures and can be used in both ip and mpls networks. This step is necessary if the rr is enabled for forwarding the rr is in the forwarding plane. This behavior promotes path diversity and reduces med oscillations.
The bgp additionalpaths install command installs the backup path if rr2 is in the forwarding plane. The path id is similar to how the rd route distinguisher works in mpls vpn, except the path ids can be used in any bgp address family. Download 400201 cisco free practice exam 101110 aug 2017. The method comprises forwarding data elements destined for the failed link via a backup path and including a loop prevention attribute in the packet. A unique path identifier is encoded into a dedicated field to the nlr i. Route reflection is optional when multiplepath advertisement is enabled in bgp. Border gateway protocol bgp routing information by peering as internal border gateway protocol ibgp instead of the widelyused external bgp peering between the pe and the ce. Bgp pic prefix independent convergence previous lesson troubleshooting bgp route advertisement. I am having one issue dont know if you can enlighten me. The bgp additional paths feature allows the advertisement of multiple paths through the same peering session for the same prefix without the new paths implicitly replacing any previous paths. Configure the vpnv4 addressfamily under the mp bgp configuration mode on the pe routers that participate in the customer vrf routing. Ive tested the backup circuit on its own and was able to see the ip routing table was being populated by my bgp beighbor.
The bgp additionalpaths select backup command triggers calculation of the backup path at rr2, which is the path via pe2. We have 31 cisco asr 9000 series manuals available for free pdf download. However, there is an extension to bgp, typically known as additionalpaths which puts an identifier on each route sent to a peer and thus enables bgp peers to exchange multiple routes to a path, thereby giving you not only a greater scope for traffic engineering, but also a. The failure recovery thread will notify bgp session threads to establish backup. Bgp installs the best and backup alternate paths for the prefixes into the bgp rib. Enabledisable selection of bgp ipv4 additional paths. When you see your own as number in the as path, we do not accept the prefix. To configure the bgp diverse path on the shadow router 4 steps are required. Enabledisable selection of bgp ipv6 additional paths. This mechanism applies at each cisco asr 9000 series aggregation services router routing configuration guide, release 5.
The backupalternate path provides a fast reroute mechanism to counter a singular network failure. One of the most interesting technologies backing up the vault networks connection to the backbone internet carriers of the americas is how we utilize border gateway protocol bgp to optimize your connection while utilizing your server. Mpls layer 3 vpn bgp as override bgp has a simple loop prevention mechanism for external bgp. In this lesson, you learn the bgp attributes and how bgp selects the best path. Im following the above article which is quite easy to understand, can someone post the configuration for the above scenario but with primary and backup links. When the bgp additional paths feature is used, what allows a bgp speaker to differentiate between the different available paths. Which ios version i can use on sw100101 to get that command running. With the addpath send pathcount 6 configuration, router r1 is configured to send up to six paths per destination to router r4.
It switches a mpls path to the backup path that was already precalcualted. This helps minimize hardware drops from competition with data plane packets. Since we would like to advertise these 2 same prefixes to internal router reflector at same time for different routing purpose, could someo. Introduction the bgp add paths capability enhances current bgp implementations by allowing a bgp router to exchange with its bgp peers more than one path for the same destinationnlri. Bgp pic edge for ip and mplsvpn cisco ios xe release 3. The remote bgp peer prepends its own nexthop address to the prefix. By introducing two vpn rrs each pe will have only two ibgp sessions. Mar 16, 2015 when we run bgp best path algorithm on the paths from each as, the algorithm will select a best path from each set of paths from that as. More specifically, this document describes extensions to bgp decision process to select backup paths in a manner that ensures the important property of consistent route selection within an as. Pic is in effect between the state of a bgp router detecting a link going down and the bgp convergence. Cisco asr 9000 series routing configuration manual pdf download. Assuming p11 is the best from as100, p21 is the best from as200, and p31 is the best from as300, then the groupbest is the set of p11, p21, and p31.
Fun with windows bgp routing the packet throwers blog. The bgp additional paths feature is a bgp extension that allows the advertisement of multiple paths for the same prefix without the new paths implicitly replacing any previous paths. After wading through windows docs for a few hours i came across this and it saved me a ton of time. We dont want any other routes added in as additionalpaths. Advertising multiple paths over ibgp sessions with bgp add paths solves those issues, depending on the way the additional paths are selected. Hi all, we have two ebgp session from customer ce to our same pe device, and we received same prefix with different community attribute, for example below. Additional paths is an extension to bgp and it adds a unique path identifier to each path.