1 00:00:00,000 --> 00:00:05,000 Now think of your router at home that gives you Internet connectivity 2 00:00:05,000 --> 00:00:09,000 in my example, I have a little British Telecom router 3 00:00:09,000 --> 00:00:13,000 that's connected to the Internet, this router doesn’t know about all the routes 4 00:00:13,000 --> 00:00:17,000 in the Internet because that is just too much for the router to handle 5 00:00:17,000 --> 00:00:22,000 so routers such as this have default gateways or default routes 6 00:00:22,000 --> 00:00:27,000 giving them access to the Internet, in the same way here 7 00:00:27,000 --> 00:00:33,000 I have the brand new Cisco router which I've connected to my Local Area Network. 8 00:00:33,000 --> 00:00:36,000 At the moment show ip route 9 00:00:36,000 --> 00:00:39,000 shows me no routes in the routing table 10 00:00:39,000 --> 00:00:44,000 because I haven’t configured any IP addresses on this router. 11 00:00:44,000 --> 00:00:46,000 show ip interface brief 12 00:00:46,000 --> 00:00:51,000 shows me that there are no IP address is configured 13 00:00:51,000 --> 00:00:53,000 on any interfaces on this router. 14 00:00:53,000 --> 00:00:57,000 So on F0/0 I’m going to configure 15 00:00:57,000 --> 00:01:06,000 an address of 192.168.1.128 as an example with /24 mask. 16 00:01:06,000 --> 00:01:13,000 That’s an IP address in the subnet used by my Internet gateway router 17 00:01:13,000 --> 00:01:15,000 I’m going to no shut the interface 18 00:01:15,000 --> 00:01:21,000 and then I’m going to test whether I can ping my VT router 19 00:01:21,000 --> 00:01:26,000 which gives me Internet access, as you can see the ping succeeds 20 00:01:26,000 --> 00:01:31,000 however, in the routing table, I only have that network 21 00:01:31,000 --> 00:01:36,000 I don’t have any other networks and I don’t have a gateway of a last resort set. 22 00:01:36,000 --> 00:01:41,000 So if I try and ping a website such as google.com 23 00:01:41,000 --> 00:01:43,000 it doesn’t work 24 00:01:43,000 --> 00:01:47,000 now that’s partly because I need to enable IP domain lookup 25 00:01:47,000 --> 00:01:54,000 and I need to tell it the DNS server that I’m going to be 26 00:01:54,000 --> 00:02:00,000 using in this case, I'll use Google, so when I try ping google.com 27 00:02:00,000 --> 00:02:05,000 it's trying to resolve that domain name with Google DNS servers 28 00:02:05,000 --> 00:02:08,000 but it’s going to timeout 29 00:02:08,000 --> 00:02:12,000 because this router doesn’t have any route in its routing table 30 00:02:12,000 --> 00:02:18,000 apart from the directly connected network 192.168.1.0 31 00:02:18,000 --> 00:02:22,000 so notice that times out, do show ip route again 32 00:02:22,000 --> 00:02:25,000 we only have that single route in the routing table 33 00:02:25,000 --> 00:02:29,000 so to solve this I can use the command IP route. 34 00:02:29,000 --> 00:02:32,000 now in this case rather than specifying the individual network 35 00:02:32,000 --> 00:02:39,000 I’m going to specify 4 0's 0.0.0.0 which is a default route 36 00:02:39,000 --> 00:02:44,000 subnet mask is going to be 4 0's as well 37 00:02:44,000 --> 00:02:48,000 I need to then specify my next hop router 38 00:02:48,000 --> 00:02:55,000 in this case, it’s my local BT internet router which is 192.168.1.254 39 00:02:55,000 --> 00:02:58,000 so show ip route 40 00:02:58,000 --> 00:03:03,000 my Cisco router only has this static route 41 00:03:03,000 --> 00:03:06,000 and a directly connected route in the routing table. 42 00:03:06,000 --> 00:03:11,000 show that again, there the 2 entries but notice the change 43 00:03:11,000 --> 00:03:16,000 gateway of last resort is 192.168.1.254 44 00:03:16,000 --> 00:03:21,000 in other words, to get to the default route my router can send traffic 45 00:03:21,000 --> 00:03:28,000 to this router, notice the little * which means candidate default route. 46 00:03:28,000 --> 00:03:31,000 so I’ve got static candidate default route 47 00:03:31,000 --> 00:03:38,000 because we've configured 0.0.0.0/0 via this IP address 48 00:03:38,000 --> 00:03:43,000 so can I now ping google.com? The answer is yes, I can. 49 00:03:43,000 --> 00:03:48,000 because this local router knows that to get to any network 50 00:03:48,000 --> 00:03:53,000 it needs to forward the traffic via this IP address. 51 00:03:53,000 --> 00:03:59,000 What about yahoo.com, that works, what about gmail.com, that works 52 00:03:59,000 --> 00:04:04,000 what about cisco.com that works 53 00:04:04,000 --> 00:04:10,000 so by using a single static route I can access networks on the Internet. 54 00:04:10,000 --> 00:04:16,000 now some websites as an example will deny ICMP messages 55 00:04:16,000 --> 00:04:21,000 so cnn.com is not allowing me to ping their website 56 00:04:21,000 --> 00:04:27,000 but I could telnet as an example to cnn.com on port 80 57 00:04:27,000 --> 00:04:31,000 and notice I’ve connected, it says it open, press enter 58 00:04:31,000 --> 00:04:34,000 how much is happening I'll press CTRL-C 59 00:04:34,000 --> 00:04:37,000 and notice I see a bunch of HTML text 60 00:04:37,000 --> 00:04:42,000 it's quite a bit information on the website 61 00:04:42,000 --> 00:04:50,000 but notice HML, so I managed to connect to cnn.com via HTTP 62 00:04:50,000 --> 00:04:56,000 because I have a static default route in the routers routing table 63 00:04:56,000 --> 00:05:01,000 forwarding traffic to a gateway of last resort.