1 00:00:19,890 --> 00:00:25,950 In this vlog, we're going to continue discussing administrative distances and the believability of 2 00:00:25,950 --> 00:00:35,910 routing protocols. So on router 1 show IP route, why in this topology is this loopback available in 3 00:00:35,910 --> 00:00:40,840 the routing table through BGP and why not for this route? 4 00:00:41,460 --> 00:00:48,600 So this network 2.2.2.2 is available in the routing table and the route was 5 00:00:48,600 --> 00:00:50,040 learnt via BGP. 6 00:00:50,980 --> 00:00:58,840 This network was learnt via EIGRP, so why is BGP used for the one network and not the other? 7 00:00:59,530 --> 00:01:01,900 The first thing you need to look at is look at this 8 00:01:01,900 --> 00:01:03,040 admin distance here. 9 00:01:03,400 --> 00:01:07,810 It's 20, so that BGP route has an administrative distance of 20. 10 00:01:08,170 --> 00:01:10,750 What are the administrative distances of BGP? 11 00:01:11,260 --> 00:01:18,570 And what you must remember is that you have two versions of BGP, EBGP and IBGP. 12 00:01:19,250 --> 00:01:21,820 EBGP has an admin distance of 20. 13 00:01:22,330 --> 00:01:28,650 IBGP has an admin distance of 200 so show IP BGP summary. 14 00:01:29,470 --> 00:01:38,380 We have a neighbor relationship to router 2 as well as to router 3. Show IP BGP neighbor 15 00:01:40,570 --> 00:01:44,420 the relationship to router 2 uses EBGP. 16 00:01:45,810 --> 00:01:51,060 Notice the autonomous system number four router 2 is 2 and scrolling down. 17 00:01:51,990 --> 00:01:59,850 This neighbor 10.1.2.2 which is router 3 is using IBGP, router 3 is an autonomous 18 00:01:59,850 --> 00:02:00,600 system one. 19 00:02:01,670 --> 00:02:03,240 The relationship is established. 20 00:02:03,920 --> 00:02:08,820 Are we learning the routes through BGP? So show IP BGP 21 00:02:09,620 --> 00:02:16,270 Yes, we are learning both the loopback of router 2 as well as the loopback of router 3 through BGP. 22 00:02:16,940 --> 00:02:24,170 So BGP has both routes in the BGP routing table but this route is not being put into the IP routing 23 00:02:24,170 --> 00:02:26,780 table and we can see that because of this 24 00:02:26,780 --> 00:02:29,110 R it says rip failure. 25 00:02:29,690 --> 00:02:35,420 The rip is the routing information base which from a CCNA point of view is the routing table. 26 00:02:35,930 --> 00:02:45,140 So this route is not put into the IP routing table by BGP and that's because a better route is available 27 00:02:45,500 --> 00:02:46,760 through EIGRP. 28 00:02:47,300 --> 00:02:53,930 So 3.3.3.3 and 4.4.4.4 are both not put into the IP routing 29 00:02:53,930 --> 00:02:54,320 table. 30 00:02:55,160 --> 00:02:59,870 Show IP BGP, we're not learning quadruple 4 through BGP. 31 00:03:00,170 --> 00:03:05,900 We are learning about this route, but because of the rip failure it's not put into the routing table. 32 00:03:06,200 --> 00:03:09,980 Notice here I the route was learned through IBGP 33 00:03:11,130 --> 00:03:19,590 and the reason why this route is not put into the routing table is because EIGRP has a lower administrative 34 00:03:19,590 --> 00:03:22,070 distance than IBGP. 35 00:03:22,650 --> 00:03:26,460 So to prove that, let's remove EIGRP from router 1. 36 00:03:27,270 --> 00:03:38,400 So rather no router EIGRP 1 show IP route notice the route is now available through BGP. 37 00:03:39,090 --> 00:03:41,370 Admin distance is 200. 38 00:03:41,850 --> 00:03:45,690 So remember, IBGP has an administrative distance of 200. 39 00:03:46,230 --> 00:03:52,800 EBGP has an admin distance of 20. If we shut the neighbor relationship down. 40 00:03:53,790 --> 00:04:00,420 So neighbor 10.1.1.2 shut down, what we should see 41 00:04:01,690 --> 00:04:07,870 is that the route is replaced by another routing protocol in this case it's OSPF. So I'm running OSPF 42 00:04:08,050 --> 00:04:14,140 from router 1 and router 2 and router 1 has learned about that loopback through OSPF previously 43 00:04:14,140 --> 00:04:20,019 because the route was learned through EBGP the EBGP route took precedence 44 00:04:20,589 --> 00:04:24,150 but now because we've shut down the neighbor relationship OSPF 45 00:04:25,730 --> 00:04:34,130 is able to add the route to the routing table. So no neighbor 10.1.1.2 shut down when that 46 00:04:34,130 --> 00:04:35,740 relationship comes up. 47 00:04:38,430 --> 00:04:47,130 Which it has, we should see the routes replaced by BGP route and we can. Now in this example rip took a long 48 00:04:47,130 --> 00:04:48,240 time to converge 49 00:04:48,480 --> 00:04:56,670 but notice RIP has been used as the routing protocol to get to this loopback rather than BGP. Rip has 50 00:04:56,730 --> 00:05:02,420 an admin distance of 120, IBGP has an admin distance of 200, rip is more believable. 51 00:05:02,880 --> 00:05:04,980 So if we removed rip 52 00:05:06,740 --> 00:05:12,860 from the router what we should see is the route is now available through BGP. 53 00:05:13,250 --> 00:05:19,350 So in summary, IBGP has an admin distance of 200, rip has an admin distance of 120, 54 00:05:19,670 --> 00:05:22,790 ISIS has an admin distance of 115, 55 00:05:23,150 --> 00:05:25,640 OSPF has an admin distance of 110, 56 00:05:25,970 --> 00:05:29,180 EIGRP internal routes have an admin distance of 90, 57 00:05:29,600 --> 00:05:36,800 static routes to next-hop addresses have a admin distance of 1, static route to directly connected interface 58 00:05:36,800 --> 00:05:38,350 as an admin distance of 0. 59 00:05:38,780 --> 00:05:42,340 The lower the number, the more believable the routing protocol. 60 00:05:42,920 --> 00:05:48,620 Remember with BGP, we have both EBGP and IBGP, 61 00:05:48,830 --> 00:05:52,970 EBGP admin distance is 20, IBGP admin distance is 200. 62 00:05:53,510 --> 00:05:55,630 Make sure you know you administrative distances. 63 00:05:56,300 --> 00:05:57,530 That concludes this vlog. 64 00:05:58,130 --> 00:05:59,990 If you've enjoyed the video, please like it 65 00:06:00,230 --> 00:06:06,260 and very importantly, please subscribe to my YouTube channel. I wish you all the very best.