1 00:00:00,860 --> 00:00:10,970 Here's another router and on this third router, using the command show ARP shows us the ARP table. I could 2 00:00:10,970 --> 00:00:16,390 ping another router in the network as follows 3 00:00:16,820 --> 00:00:23,330 and now when I use the command show up, there's the resolution between IPv4 address and 4 00:00:23,330 --> 00:00:29,900 MAC address of the remote router. Show IP route shows us the routing table 5 00:00:30,320 --> 00:00:37,340 and as you can see, this router has a default gateway or gateway of last resort of 192.1 6 00:00:37,340 --> 00:00:38,810 68.1.249. 7 00:00:39,940 --> 00:00:45,430 So there's the static default gateway, so this router as an example, will be able to ping 8 00:00:46,920 --> 00:00:52,890 google.com after doing a DNS request to the DNS server. 9 00:00:54,080 --> 00:01:04,550 So that IP address wasn't previously in the ARP cache over here, but show ARP now shows us the resolution 10 00:01:04,550 --> 00:01:10,100 between IPv4 address and MAC address of this local DNS server. 11 00:01:10,670 --> 00:01:18,410 The router was able to ping google.com because it sent traffic to google via its default gateway 12 00:01:18,740 --> 00:01:23,290 or gateway of last resort, 192.168.1.249. 13 00:01:23,780 --> 00:01:28,370 So the router has both an ARP cache as well as a routing table. 14 00:01:29,370 --> 00:01:37,290 We can see details of interfaces on this router by using the command show IP interface brief and we 15 00:01:37,290 --> 00:01:40,170 can see more detail by looking at an individual interface. 16 00:01:41,130 --> 00:01:47,280 So this FastEthernet interface is configured with this hardware MAC address which is the same as 17 00:01:47,280 --> 00:01:54,840 the burnt-in MAC address sent by Cisco on this interface, the speed, and duplex of the interface is a 100 18 00:01:54,840 --> 00:02:01,590 megabits per second, and it's using full-duplex, ARP entries will time out after 4 hours by default 19 00:02:01,770 --> 00:02:02,670 on this router. 20 00:02:03,270 --> 00:02:04,680 Notice we can see the input 21 00:02:04,680 --> 00:02:05,340 queue 22 00:02:06,620 --> 00:02:14,060 for the interface as well as the output queue. So packets may need to be buffered as an example on egress 23 00:02:14,510 --> 00:02:22,190 out of the FastEthernet interface, if there's high congestion, we can see the packets in and packets 24 00:02:22,580 --> 00:02:29,210 output on this interface, but interfaces on routers have buffers if packets need to be buffered before 25 00:02:29,210 --> 00:02:35,540 they're sent or buffered when they received and before they can be processed by the central CPU of the router. 26 00:02:37,030 --> 00:02:38,800 Show version on this router 27 00:02:41,440 --> 00:02:46,630 will show us that the memory on this router is a lot lower than the other routers. 28 00:02:47,830 --> 00:02:49,750 So 115 29 00:02:51,190 --> 00:02:55,090 712 plus 15360 30 00:02:57,660 --> 00:03:07,410 divided by 1024 shows us that this router only has 128 meg of RAM, whereas the other routers had 256 meg 31 00:03:07,410 --> 00:03:13,050 of RAM show Flash shows us the files stored in Flash on this router 32 00:03:13,650 --> 00:03:23,970 notice they are two versions of the operating system on the strata and commands such as the boot command. 33 00:03:25,010 --> 00:03:32,430 Allow us to specify which operating system is going to be booted or loaded by the router, by default 34 00:03:32,450 --> 00:03:35,180 the first operating system in Flash is loaded 35 00:03:35,510 --> 00:03:43,400 but in this case, the boot system flash command specifies that this operating system, instead of this 36 00:03:43,400 --> 00:03:46,010 operating system, should be loaded by the router. 37 00:03:46,940 --> 00:03:50,660 Now, in this case, they're the same notice the name is slightly different. 38 00:03:50,990 --> 00:03:56,960 Underscore two, but you could have different operating systems in Flash or different versions of an 39 00:03:56,960 --> 00:04:01,140 operating system and then decide which one gets booted. 40 00:04:01,760 --> 00:04:06,650 So if you're upgrading the router, you may load an additional operating system into Flash and then 41 00:04:06,650 --> 00:04:08,360 the router to boot off that 42 00:04:08,540 --> 00:04:12,350 but if it fails, then boot off an alternate operating system.