BGP

BGP4-1 Copyright © 2005 Juniper Networks, Inc. Proprietary and Confidential www.juniper.net BGP Operation  BGP stores routes in three main routing information base (RIB) memory tables •Adjacency-RIB-IN: Contains all received routes from each peer •RIB-LOCAL: Contains routes the local router uses to forward traffic •Adjacency-RIB-OUT: Contains all advertised routes sent to each peer  Only active BGP routes in the local routing table can be advertised to peers •Single, best BGP path is advertised •Can use advertise-inactive when BGP route is not active, but only the single, best, inactive BGP path is advertised © 2008 Juniper Networks, Inc. All rights reserved. 2 BGP Update Message  Advertised and withdrawn routes are sent in an update message to established peers •Common BGP header fields: • (16-byte) Marker • (2-byte) Length • (1-byte) Type •Update message fields: • (2-byte) Unfeasible routes length • (Variable) Withdrawn routes • (2-byte) Total path attributes length • (Variable) Path attributes • (Variable) Network layer reachability information © 2008 Juniper Networks, Inc. All rights reserved. 3 Local Preference  Often used to set the exit point from an autonomous system •Only exchanged within the confines of a single AS • (1-byte) Attribute type • (Variable) Attribute length • (4-byte) Local preference value © 2008 Juniper Networks, Inc. All rights reserved. 4 Inc. 5 .AS Path  Collection of autonomous system numbers through which the route has passed •Used to prevent routing loops •Used to select an active BGP path • (2-byte) Attribute type • (Variable) Attribute length • (Variable) AS path segments © 2008 Juniper Networks. All rights reserved. All rights reserved. 6 .Origin  Measure of believability set by the originating BGP router •Internal (0) > External (1) > Incomplete (2) •JUNOS software sets all injected routes to Internal • (2-byte) Attribute type • (1-byte) Attribute length • (1-byte) Origin © 2008 Juniper Networks. Inc. Inc. All rights reserved. 7 .Multiple Exit Discriminator  Often used to set an incoming entry point for an AS •Never passed through one AS to another AS •Can be translated from IGP metric • (2-byte) Attribute type • (1-byte) Attribute length • (4-byte) Multiple exit discriminator © 2008 Juniper Networks. Can the BGP next hop be reached? •If yes. proceed •If no. 8 . Prefer the highest local preference value 3. Prefer the shortest AS path length 4. Prefer the lowest origin value 5. All rights reserved.BGP Path Selection Process (1 of 2)  Steps: 1. Prefer paths learned via EBGP over routes learned via IBGP © 2008 Juniper Networks. Prefer the lowest MED value 6. Inc. stop processing 2. When routes from different AS’ are equal up to the RID comparison stage.3 for the BGP next hop. Prefer paths from the peer with the lowest RID a.Prefer paths from the peer with the lowest peer ID © 2008 Juniper Networks. prefer currently active route 10. For preference ties within the same routing table. Examine routing tables inet. Install the physical next hop(s) for the route with the better preference b.3 c. In the event of a preference tie. Prefer paths with the lowest IGP metric. Inc. Select a physical next hop (or hops) for each peer a.BGP Path Selection Process (2 of 2) 7. 9 . install the physical next hop(s) found in inet. install the physical next hop(s) where the greater number of equal-cost paths exist 8. Prefer paths with the shortest cluster list length 9. All rights reserved.0 and inet. 32.29.2 via fe-0/0/0. All rights reserved. 0 holddown.1+1042 AS path: 65000 I Localpref: 200 Router ID: 192.29.168.222.48.222. 94 routes (52 active.2+1061 AS path: 65000 I ---(more)--- © 2008 Juniper Networks. 1 announced) *BGP Preference: 170/-201 Source: 192. selected State: <Ext> Inactive reason: Local Preference Local AS: 65432 Peer AS: 65000 Age: 19:09 Task: BGP_65000.48/24 detail inet.1 Next hop: 10.168.168.2 via ge-0/1/0.0/24 (3 entries.32.0: 52 destinations. selected Protocol next hop: 192. 10 .Local Preference Selection user@host> show route 192.168.28. 0 hidden) 192.168.29.32.10.0.0.1 Indirect next hop: 858b4e0 73 State: <Active Int Ext> Local AS: 65432 Peer AS: 65432 Age: 18:57 Metric2: 3 Task: BGP_65432.222. Inc.222.2 Next hop: 10.192.1 BGP Preference: 170/-101 Source: 10.168.32. 45.45.1 Indirect next hop: 85d8270 46 State: <Active Int Ext> Local AS: 65432 Peer AS: 65432 Age: 3:41 Metric2: 3 Task: BGP_65432.0: 52 destinations.1+179 AS path: 65000 I Localpref: 100 Router ID: 192. Inc.0.16.168.192. All rights reserved.AS Path Selection user@host> show route 192.16. 11 .168.45. 1 announced) *BGP Preference: 170/-101 Source: 192.1 BGP Preference: 170/-101 Source: 10.222. selected State: <Ext> Inactive reason: AS path Local AS: 65432 Peer AS: 65000 Age: 25 Task: BGP_65000.48/24 detail inet.1 via so-0/3/0. 0 hidden) 192.44.168.222.16.16.1 via fe-0/0/0.1 Next hop: 10. selected Protocol next hop: 192.0.222.0/24 (3 entries. 0 holddown.168.168. 94 routes (52 active.10.1+1064 AS path: 65000 65000 65000 I ---(more)--- © 2008 Juniper Networks.1 Next hop: 10.48.222.168. 222.1 via fe-0/0/1.168.222.6. 74 routes (52 active.48/24 detail inet.1 Next hop: 10. selected State: <Active Ext> Local AS: 65432 Peer AS: 65000 Age: 1:29 Metric: 20 Task: BGP_65000.1 via so-0/3/0. Inc.10.6.Origin Selection user@host> show route 192.168.45.222. 1 announced) *BGP Preference: 170/-101 Source: 10. 0 hidden) 192.1+1064 AS path: 65000 ? Localpref: 100 ---(more)--- © 2008 Juniper Networks.6.168.1 BGP Preference: 170/-101 Source: 10.45.48.222.45.1+1084 AS path: 65000 I Localpref: 100 Router ID: 192. All rights reserved.0/24 (2 entries.0: 52 destinations. 12 . selected State: <Ext> Inactive reason: Origin Local AS: 65432 Peer AS: 65000 Age: 53 Task: BGP_65000.1 Next hop: 10.0.222.48.222.0.10. 0 holddown. 1+179 AS path: 65000 I Localpref: 100 Router ID: 192.16.MED Selection user@host> show route 192.0/24 (3 entries.222.168.1 Indirect next hop: 85d8270 46 State: <Active Int Ext> Local AS: 65432 Peer AS: 65432 Age: 9:53 Metric: 5 Metric2: 3 Task: BGP_65432.192.222.1 via so-0/3/0. 94 routes (52 active. Inc.1 Next hop: 10.10.168.1+1064 AS path: 65000 I ---(more)--- © 2008 Juniper Networks.48. 0 holddown.1 via fe-0/0/0. 13 .45.45.168. selected Protocol next hop: 192. 0 hidden) 192. All rights reserved.1 Next hop: 10. 1 announced) *BGP Preference: 170/-101 Source: 192.222.0.168.168.45.1 BGP Preference: 170/-101 Source: 10.168.44.16.0. selected State: <NotBest Ext> Inactive reason: Not Best in its group Local AS: 65432 Peer AS: 65000 Age: 2:21 Metric: 20 Task: BGP_65000.16.0: 52 destinations.222.16.48/24 detail inet. 5.1 Next hop: 10. 1 announced) *BGP Preference: 170/-101 Source: 10. 14 .168. Inc.32.52.28. 0 holddown.2+1067 AS path: 65000 I Localpref: 100 Router ID: 192.32. selected State: <Active Ext> Local AS: 65432 Peer AS: 65000 Age: 2:18 Task: BGP_65000.222.1+1042 AS path: 65000 I ---(more)--- © 2008 Juniper Networks.0.0: 52 destinations.EBGP over IBGP Selection user@host> show route 192. 73 routes (52 active.222.5. All rights reserved.5.222.1 BGP Preference: 170/-101 Source: 192.10. 0 hidden) 192.2 Next hop: 10.32.168.0.168.222.2 via fe-0/0/2. selected Protocol next hop: 192.168.2 via fe-0/0/0.0/24 (2 entries.192.48/24 detail inet.168.48.1 Indirect next hop: 858b4e0 73 State: <NotBest Int Ext> Inactive reason: Interior > Exterior > Exterior via Interior Local AS: 65432 Peer AS: 65432 Age: 5:25 Metric2: 3 Task: BGP_65432.168. 32.168.1+1126 AS path: 65000 I Localpref: 100 Router ID: 192.168.IGP Cost Selection user@host> show route 192.16.16.16.168.32.168. 0 hidden) 192.1 Next hop: 10.0.168. 1 announced) *BGP Preference: 170/-101 Source: 192.48.168.32.1 Indirect next hop: 85d630c 44 State: <NotBest Int Ext> Inactive reason: IGP metric Local AS: 65432 Peer AS: 65432 Age: 3:19 Metric2: 2 Task: BGP_65432.0: 49 destinations. selected Protocol next hop: 192.1 via fe-0/0/0.1 BGP Preference: 170/-101 Source: 192.168. 69 routes (49 active.192.1+1045 ---(more)--- © 2008 Juniper Networks.168.1 Indirect next hop: 85d61d4 41 State: <Active Int Ext> Local AS: 65432 Peer AS: 65432 Age: 12 Metric2: 1 Task: BGP_65432. Inc.28.168.16.222.0/24 (2 entries.48/24 detail inet.4. selected Protocol next hop: 192.222. 15 .0.1 Next hop: 10. 0 holddown. All rights reserved.192.2 via fe-0/0/1. 1 announced) *BGP Preference: 170/-101 Next hop: 10.2 1.2.1 Localpref: 100 Router ID: 192.168.1 © 2008 Juniper Networks.1. selected Protocol next hop: 192.1 Indirect next hop: 85d83a8 72 State: <NotBest Int Ext> Inactive reason: Cluster list length Local AS: 65000 Peer AS: 65000 Age: 1:13 Metric: 20 Metric2: 3 AS path: 65432 I (Originator) Cluster list: 2.1 Localpref: 100 Router ID: 192.44.1 via fe-0/0/1.36. 16 . Inc.1 Indirect next hop: 85d8270 70 State: <Active Int Ext> Local AS: 65000 Peer AS: 65000 Age: 6:41 Metric: 20 Metric2: 3 AS path: 65432 I (Originator) Cluster list: 3.0.0.168.20.0: 42 destinations.1.3.168. 47 routes (42 active.3.1 AS path: Originator ID: 192.6.168.24. 0 hidden) 192.168.16.Cluster List Length Selection user@host> show route 192.222.16/24 detail inet.1 via fe-0/0/0.2.24.222. 0 holddown.1 BGP Preference: 170/-101 Next hop: 10. selected Protocol next hop: 192.20.168.0/24 (2 entries.3 AS path: Originator ID: 192. All rights reserved.168.168.48. 2+179 AS path: 65000 I Localpref: 100 Router ID: 192. selected State: <Active Ext> Local AS: 65432 Peer AS: 65000 Age: 10 Task: BGP_65000. 17 .168.48/24 detail inet.10.10.168.2 Next hop: 10. selected State: <NotBest Ext> Inactive reason: Router ID Local AS: 65432 Peer AS: 65000 Task: BGP_65000.29. Inc.29.29.5.1 ---(more 66%)--- © 2008 Juniper Networks.0. 0 holddown.48.20.222.222.2 via ge-0/1/0.2 via fe-0/0/2. All rights reserved. 1 announced) *BGP Preference: 170/-101 Source: 10.0.5.222.168.222.Router ID Selection user@host> show route 192.222.1 BGP Preference: 170/-101 Source: 10.2 Next hop: 10.222.0/24 (3 entries.52. 0 hidden) 192.5.168.2+1067 AS path: 65000 I Localpref: 100 Router ID: 192.0: 52 destinations. 94 routes (52 active. 106 routes (64 active.5. Inc.2 Next hop: 10.15.0.5.15.222.52.222.15. 0 hidden) 192.168.52.1.48. selected State: <NotBest Ext> Inactive reason: Update source Local AS: 65432 Peer AS: 65000 Task: BGP_65000.222. All rights reserved.1 BGP Preference: 170/-101 Source: 10. selected State: <Active Ext> Local AS: 65432 Peer AS: 65000 Age: 30 Task: BGP_65000. 18 . 1 announced) *BGP Preference: 170/-101 Source: 10.2 via fe-0/0/2.2 Next hop: 10.222.168.222.0/24 (3 entries.1 ---(more 51%)--- © 2008 Juniper Networks. 0 holddown.48/24 detail inet.2+179 AS path: 65000 I Localpref: 100 Router ID: 192.0: 64 destinations.222.Peer ID Selection user@host> show route 192.2 via fe-0/0/2.168.5.10.168.2+1073 AS path: 65000 I Localpref: 100 Router ID: 192.10. } © 2008 Juniper Networks.1/24 (AS1) 10.1.Path Selection: Peer ID  Used when multiple BGP peering sessions exist between two routers •Only one BGP session is used to forward traffic •ID is the physical IP address on the neighboring router’s interface Los Angeles 10.2.2/24 10. peer-as 2.10. Inc.1/24 Las Vegas (AS2) [edit protocols bgp group ext-peers] type external.1.10.2. neighbor 10.10.1.2/24 10.1. neighbor 10. All rights reserved.10.2. 19 .1.10.10. 29.29.28. neighbor 10.BGP Multipath (1 of 3)  BGP can ignore both router ID and peer ID comparisons when multipath is configured within BGP •Can use: • Two peering sessions to the same router • Two peering sessions to different routers in the same AS Los Angeles (AS1) 10.2.2 2 7 7 10.222.222.28. Inc.28.2 2 8 10 © 2008 Juniper Networks. 10.2/24 OutQ 0 0 (AS2) Flaps Last Up/Dwn State|#Active/Rec 0 00:00:02 4/4/0 0 00:00:06 0/4/0 20 .29.222.222. peer-as 2. } user@host> show bgp summary Peer AS InPkt OutPkt 10.1/24 [edit protocols bgp group ext-peers] type external. All rights reserved.222.28. neighbor 10.2/24 Las Vegas (AS2) Reno 10.222.2.222.222.1/24 10.29. 2 2 I B 170 100 >10. * = Both A Destination P Prf Metric 1 * 172. Metric 2 Next hop AS path 21 .222.20.2 2 I B 170 100 >10.28.2 2 I B 170 100 >10. Inc.28.2 2 I * 172.28.BGP Multipath (2 of 3)  Routes from each peer contain a single next hop user@host> show route protocol bgp terse inet.= Last Active.29.20.222. 0 hidden) + = Active Route.222.222.222.2 2 I B 170 100 >10. All rights reserved. .28.29.16. 0 holddown.222.222.8/30 * 172.2 2 I B 170 100 >10.2 2 I B 170 100 >10.16/30 © 2008 Juniper Networks. 19 routes (15 active.20.29.222.20.4/30 B 170 100 >10.0: 15 destinations.12/30 * 172.16.2 2 I B 170 100 >10.16.16.29. 2 >10.222.29.20.16.2 10.222.222.29.2 AS path 2 I 2 I 2 I 2 I 2 I 2 I 2 I 2 I 22 .28.8/30 B 170 B 170 100 100 * 172.222.222.2 >10.222.29.28.29.28.12/30 B 170 B 170 100 100 * 172.29.2 10. .4/30 P Prf B 170 Metric 1 100 * 172.222.2 >10.2 >10.28.222.16/30 B 170 B 170 100 100 B 170 100 © 2008 Juniper Networks.20.BGP Multipath (3 of 3)  Peer group on Los Angeles configured with multipath •Active route receives two next hops •Forwarding table still maintains a single next hop per route user@host> show route protocol bgp terse inet.16. 0 holddown.16.= Last Active.0: 15 destinations.222. * = Both A Destination * 172. All rights reserved.20.2 >10.29.29. 0 hidden) + = Active Route.222.222. 19 routes (15 active.29.20.2 10.2 >10.2 >10. Metric 2 Next hop >10. Inc.222.2 10.16. 10.10.10.1.16.1/24 (AS1) 10.4.Multihop Peering  EBGP sessions can peer with nonphysical addresses lo0: 192.128. Step 1 local-address 192.2. } © 2008 Juniper Networks. Inc. All rights reserved.128.2.10.1.1 Los Angeles 10.1 next-hop [ 10. a loopback address on a directly connected peer—higher values are needed } for peers that are not directly connected [edit routing-options] static { Step 3 route 172.2.1 { A TTL value of 1 accommodates peering to Step 2 multihop ttl 1.2/24 10.128.3.2/24 10.4 lo0: 172.168.1/24 Las Vegas (AS2) [edit protocols bgp group ext-peers] type external.16.10. neighbor 172.1 10.1.3. 23 .1 ].16.10.168. 4/30 Type Index NhRef Netif indr 106 4 ucst 47 4 fe-0/0/0.10.4/30 P Prf B 170 Metric 1 100 B 170 100 Metric 2 user@host> show route forwarding-table matching Routing table: inet Internet: Destination Type RtRef Next hop 172.1.Multiple Next Hops  Both multihop and multipath create routes with multiple next hops in the routing table •Use a routing policy to forward traffic on both next hops user@host> show route 172.1 © 2008 Juniper Networks.1 >10. Inc. * = Both A Destination * 172.16. 0 hidden) + = Active Route.1 10.0 24 .10. All rights reserved.2.4/30 user 0 10.2.16. . 19 routes (15 active.16. Next hop >10.16.1. 0 holddown.10.4/30 terse inet.20.1 AS path 2 I 2 I 172.0: 15 destinations.20.= Last Active.10.20.20. } user@host> show configuration routing-options forwarding-table export load-balance.10.= Last Active.4/30 terse inet. 0 hidden) + = Active Route.20.10.10.10.Load Balancing user@host> show configuration policy-options policy-statement load-balance then { load-balance per-packet. 25 .20.1.10.0 © 2008 Juniper Networks. Inc.4/30 P Prf B 170 Metric 1 100 B 170 100 Metric 2 Next hop >10.16.1. All rights reserved. 19 routes (15 active.1 ucst 99 4 ge-0/1/0.4/30 Routing table: inet Internet: Destination Type RtRef Next hop Type Index NhRef Netif 172.20. .16.1 10.20.1 ucst 47 4 fe-0/0/0.0: 15 destinations. * = Both A Destination * 172.16.2. user@host> show route 172.0 indr 107 2 10.1 >10.4/30 user 0 ulst 108 4 indr 106 2 10.16. 0 holddown.1 AS path 2 I 2 I user@host> show route forwarding-table matching 172.2.2. 16.1 © 2008 Juniper Networks.168. All rights reserved.32.16.168.168.1 Montreal 192.1.0/24 route is advertised into AS 65002 by an EBGP peer 172.1 26 .20. San Jose 192.168.16.1. Inc.1 Amsterdam 192.Multihop with No Next-Hop Change (1 of 4)  AS 65001 and 65002 wants to use MPLS for forwarding user traffic •LSP from Hong Kong to Amsterdam is one example  The 172.0/24 via EBGP AS 65001 AS 65002 LSP Hong Kong 192.40. 16.1 Next hop: 10.222.29. All rights reserved. 0 hidden) + = Active Route.1.168.3 routing table lab@HongKong> show route table inet.0/24 route currently does not use the LSP to Amsterdam •BGP next hop is not in the inet. 0 holddown.168. label-switched-path HK-to-Amsterdam lab@HongKong> show route 172.Multihop with No Next-Hop Change (2 of 4)  The 172. 0 hidden) 172.2 via ge-0/1/0.16/16 detail inet.0/24 (1 entry.3 inet.0.192.20. 27 .0: 14 destinations.2 via ge-0/1/0.168.1 Indirect next hop: 858709c 119 State: <Active Int Ext> Local AS: 65001 Peer AS: 65001 Age: 26:02 Metric2: 0 Task: BGP_65001.1.29. Inc.3: 1 destinations. 16 routes (14 active.0 AS path: 65002 65003 I Localpref: 100 Router ID: 192. * = Both 192. 0 holddown. .1 © 2008 Juniper Networks.168.168.40. 1 routes (1 active. 1 announced) *BGP Preference: 170/-101 Source: 192.20.= Last Active.32.1/32 *[RSVP/7] 00:14:02.1+3187 Announcement bits (2): 0-KRT 2-Resolve inet.16. selected Protocol next hop: 192. metric 0 > to 10.0.222.20. 0 holddown. Inc.1.1 multihop no-nexthop-change user@Montreal> show route advertising-protocol bgp 192. you can change default •The next-hop value is the address of the IBGP peer that first advertised the route user@Montreal> show route advertising-protocol bgp 192.1 inet.16.168. 1 hidden) Prefix Nexthop MED Lclpref AS path * 172.1. 28 . 16 routes (14 active.0/24 192.20.Multihop with No Next-Hop Change (3 of 4)  EBGP peers alter the BGP next hop across AS boundaries •The show route advertising-protocol bgp command has a next-hop value of self  If you use multihop and the keyword. All rights reserved.1 65003 I © 2008 Juniper Networks.0: 14 destinations.16. 1 hidden) Prefix Nexthop MED Lclpref AS path * 172.168.168.32.168.0/24 Self 65003 I [edit protocols bgp group ext-peers] user@Montreal# set neighbor 192.1 inet. no-nexthopchange.20.0: 14 destinations. 0 holddown.20. 16 routes (14 active. 739 ms 0.6.868 ms 0. 0 hidden) + = Active Route.16/16 inet.29.0/24 user@HongKong> show route table inet. * = Both 192.851 ms MPLS Label=100008 CoS=0 TTL=1 S=1 3 10.16.2) 0.20.1.1.2 (10.16. 0 holddown.168.1. label-switched-path HK-to-Amsterdam user@HongKong> show route 172.682 ms 0.29.222.16.2 (10.16.Multihop with No Next-Hop Change (4 of 4)  User traffic uses the LSP to reach 172.6. 30 hops max. 40 byte packets 1 10.1) 0.734 ms 0. 29 .222.1.2) 1.1 (172.222. label-switched-path HK-to-Amsterdam user@HongKong> traceroute 172.168.= Last Active.3 inet.1. .2 via ge-0/1/0.687 ms 0.831 ms MPLS Label=100010 CoS=0 TTL=1 S=1 2 10.1.222.1.0/24 *[BGP/170] 01:33:20. from 192.1.2 (10.1/32 *[RSVP/7] 01:21:26.16.222.0.29.168. 16 routes (14 active.1 traceroute to 172.16.29.2 via ge-0/1/0. metric 0 > to 10. localpref 100.1) from 192.0: 14 destinations. 0 hidden) + = Active Route.0.222.222.690 ms © 2008 Juniper Networks.641 ms 4 10.3: 1 destinations.1 AS path: 65002 65003 I > to 10. 1 routes (1 active.168.1 source 192.16. 0 holddown.913 ms 0.32. .= Last Active.45. All rights reserved. Inc.222.916 ms 0.45.114 ms 0.222.1 (10.222. * = Both 172.2) 0. 10. } • Can enable MD5 authentication [edit protocols bgp] group ext-peers { type external. neighbor 10. peer-as 65000.10.10/16. peer-as 2.10. } }  allow accepts open messages from any peer within the configured IP address range [edit protocols bgp] group ext-peers { type external.Peer Configuration Options (1 of 3)  passive keeps BGP from sending open message [edit protocols bgp] group ext-peers { type external.1 { authentication-key “$9$. Inc.mQn/9pBRSAp7VYojiAp0O1h”. allow 10. peer-as 2. neighbor 10. } } © 2008 Juniper Networks. 30 .1 { passive.10. All rights reserved. peer-as 2.10.Peer Configuration Options (2 of 3)  prefix-limit allows a specified amount of prefixes to be received [edit protocols bgp] group ext-peers { type external.10.1. Inc. } © 2008 Juniper Networks. All rights reserved. teardown 80 idle-timeout 10. } } } neighbor 10. hold-time 45. family inet { unicast { prefix-limit { maximum 25000. neighbor 10. peer-as 2.1.10. 31 . }  hold-time alters the value used in the session negotiation process [edit protocols bgp] group ext-peers { type external.10. 1.10. } © 2008 Juniper Networks. All rights reserved. peer-as 2. 32 .10. Inc.Peer Configuration Options (3 of 3)  advertise-peer-as disables suppression of route advertisements •Routes learned from an EBGP peer are advertised back to the same EBGP peer •Routes learned from an EBGP peer are advertised to EBGP peers in the same AS as the originating peer [edit protocols bgp] group ext-peers { advertise-peer-as. neighbor 10. Inc.Graceful Restart  A BGP router can negotiate with peers to maintain its announced routes during a restart •Neighbors continue forwarding traffic to the router •Neighbors do not withdraw the routes of the restarting router  End-of-RIB markers sent for each NLRI •Notifies the neighbor that all current routing information was sent •Local router defers path selection algorithm until the marker is received  Configured globally within [edit routingoptions] © 2008 Juniper Networks. 33 . All rights reserved. 0 holddown.Modifying Local Preference AS 65002 AS 65003 192.0: 14 destinations. 0 hidden) Restart Complete Prefix Nexthop MED Lclpref AS path * 192.0/24 local-preference user@host> show route advertising-protocol bgp 192.19.168.0/24 Self 0 100 65003 I [edit] user@host# set protocols bgp group int-peers local-preference 300 user@host> show route advertising-protocol bgp 192.1 inet. 0 hidden) Restart Complete Prefix Nexthop MED Lclpref AS path * 192.168. 34 .0: 14 destinations. All rights reserved. 15 routes (14 active.168.1 inet.168.19. Inc.0/24 Self 0 300 65003 I © 2008 Juniper Networks. 15 routes (14 active.168.40. 0 holddown.40.19. 0/24 192.168.168.17.168.17.0/24: 1000 192.19.19.0/24 192.0/24: 1000 192. 35 . All rights reserved.168.0/24: 1000 remove-private AS 1000 192.18.0/24 © 2008 Juniper Networks.168.19.Modifying AS Path: remove-private 192.168.168.0/24: 65002 192.18.168. Inc.17.0/24: 65003 AS 65001 AS 65002 AS 65003 192.0/24: 65001 192.18.168. 16.0/24 36 .16. Inc.0/24: 222 AS 222 172.0/24: 1 222 Internet 172.10.10.0/24 © 2008 Juniper Networks.Modifying AS Path: local-as (1 of 3) 172.16.0/24: 333 AS 333 172. 172.0/24: 1 333 AS 1 172.12.12.16.10.16.12.16. All rights reserved. 37 .10.0/24: 333 AS 222 AS 333 172. Inc.Modifying AS Path: local-as (2 of 3) AS 777 172.16.10.16.12.16.10.10.0/24 © 2008 Juniper Networks.0/24: 222 Internet 172.16. All rights reserved.0/24: 1 222 172.12.12.12.16.0/24: 1 333 172.0/24: 777 1 222 172.16.0/24: 777 1 333 local-as 1 172.0/24 172.16.16. 16.Modifying AS Path: local-as (3 of 3) AS 777 172.16.12.16.12.10.0/24: 777 333 local-as 1 private 172.16.10.10. Inc.16.0/24: 333 172.0/24: 222 172.12. 38 .0/24: 333 AS 222 AS 333 172.16.0/24 172.10.0/24 © 2008 Juniper Networks.0/24: 222 Internet 172.0/24: 777 222 172.16.16.12. All rights reserved. 8 routes (8 active.222.1 172.1 AS path 65432 65432 I © 2008 Juniper Networks. 39 .16.222.16. 0 hidden) Prefix Nexthop MED Lclpref * 172. 0 holddown.10.0: 8 destinations.0: 8 destinations.4.0/24: 65022 172.0/24 10. 0 hidden) Prefix Nexthop MED Lclpref * 172.10.10.2 inet.4.222.4.1 inet.4.4. 8 routes (8 active. 8 routes (8 active.0/24 AS 65432 as-override user@AS65432> show route advertising-protocol bgp 10.222. All rights reserved.222.4.16. 0 hidden) [edit] user@AS65432# set protocols bgp group AS-65022 as-override user@AS65432> show route advertising-protocol bgp 10.16.16.16.10.222.10.1 inet. 0 holddown. 0 holddown.10. Inc.2 inet.0/24 Self AS path 65022 I user@AS65022> show route receive-protocol bgp 10.0/24: 65432 65432 10.222. 0 holddown. 7 routes (7 active.Modifying AS Path: as-override 172.0/24 Self AS path 65022 I user@AS65022> show route receive-protocol bgp 10.0: 8 destinations. 0 hidden) Prefix Nexthop MED Lclpref * 172.0: 7 destinations.2 AS 65022 AS 65022 10.4. AS path 65432 65022 I 40 . 0 hidden) Prefix Nexthop MED Lclpref * 172.Modifying AS Path: loops 172.4.10.0/24 172.10.16.1 © 2008 Juniper Networks.10.0/24: 65022 AS 65022 172.0: 7 destinations.222.16.10.222.0: 8 destinations. 0 holddown.4.1 inet.16. 0 hidden) [edit] user@AS65022# set routing-options autonomous-system 65022 loops 2 user@AS65022> show route receive-protocol bgp 10. 8 routes (8 active.1 inet.222.16. 7 routes (7 active. 0 holddown.4. Inc.0/24: 65432 65022 AS 65432 AS 65022 user@AS65022> show route receive-protocol bgp 10.0/24 10. All rights reserved. 168. neighbor 192.3 neighbor 192.5 } © 2008 Juniper Networks.168.3.4 neighbor 192. Inc.2.2 neighbor 192. 41 .Coordinating MED and IGP Metrics  Use the metric-out command with a group or neighbor •Can be set to: • A specific value • The current IGP metric • The minimum IGP metric ever learned •Can add to or subtract from the IGP metric [edit protocols bgp] group as-100-peers { type external. igp.168. All rights reserved.4.168.5. peer-as 100. minimum-igp. igp 5. metric-out metric-out metric-out metric-out 10. 42 . regardless of neighbor AS cisco-non-deterministic Use Cisco IOS nondeterministic path selection algorithm © 2008 Juniper Networks. regardless of whether the neighboring AS is the same •Use with caution—every network has a different interpretation of a good MED  cisco-non-deterministic compares paths based on when they are received •Not recommended for use in your network •Can cause incorrect route selections [edit] user@host# set protocols bgp path-selection ? Possible completions: always-compare-med Always compare MED values.Path Selection and MEDs  By default. the JUNOS software uses a deterministic MED comparison scheme for routes from the same AS  always-compare-med compares MED values. Inc. All rights reserved.