蛋汤 2007-11-12 11:41
配置BGP的缺省路由
[align=center][size=3][font=宋体]实验[/font][font=Times New Roman]9.11.1
[/font][font=宋体]配置[/font][font=Times New Roman]BGP[/font][font=宋体]的缺省路由[/font][/size][/align]
[size=3][font=宋体]一、实验拓扑[/font][font=Times New Roman]:[/font][/size]
[font=Times New Roman][size=3] [img]http://p.blog.csdn.net/images/p_blog_csdn_net/ieeenjoy/291908/o_9111.jpg[/img][/size][/font]
[font=宋体][size=3]二、实验目的：[/size][/font]
[size=3][font=Times New Roman] [/font][font=宋体]作为世界级顶级[/font][font=Times New Roman]IT[/font][font=宋体]网络培训公司的[/font][font=Times New Roman]ITAA[/font][font=宋体]在招标之后决定接入两家[/font][font=Times New Roman]ISP[/font][font=宋体]，分别为[/font][font=Times New Roman]ISP1[/font][font=宋体]和[/font][font=Times New Roman]ISP2,[/font][font=宋体]由这两家[/font][font=Times New Roman]ISP[/font][font=宋体]为[/font][font=Times New Roman]ITAA[/font][font=宋体]提供非洲的互联网内容接入，而[/font][font=Times New Roman]ITAA[/font][font=宋体]为其提供亚太地区的接入，本案例中，只考虑如何保证[/font][font=Times New Roman]ITAA[/font][font=宋体]能够不间断，有保障的接入非洲互联网。[/font][/size]
[size=3][font=Times New Roman] [/font][font=宋体]方案：主要流量通过[/font][font=Times New Roman]ISP1[/font][font=宋体]出去，[/font][font=Times New Roman]ISP2[/font][font=宋体]做备用（无间断备用，不惜一切代价保证[/font][font=Times New Roman]ITAA[/font][font=宋体]每分每秒的不间断接入）。[/font][/size]
[size=3][font=Times New Roman] [/font][font=宋体]目录：[/font][/size]
[table][tr][td=1,1,307][font=宋体][size=3]－基本链路配置[/size][/font]
[size=3][font=宋体]－安全配置：限制[/font][font=Times New Roman]ISP1 [/font][font=宋体]和[/font][font=Times New Roman] ISP 2[/font][font=宋体]互通[/font][/size]
[font=宋体][size=3]－尝试方案：配置两条静态路由；[/size][/font]
[font=宋体][size=3]－最终方案：配置默认路由，再配一条静态路由；[/size][/font]
[font=宋体][size=3]－结论[/size][/font]
[font=宋体][size=3]－[color=red]一些未解疑问[/color][/size][/font]
[/td][/tr][/table][font=宋体][size=3]三、实验开始：[/size][/font]
[size=3][font=Times New Roman] [/font][font=宋体]基本链路配置[/font][font=Times New Roman]:[/font][/size]
[align=center][table=529][tr][td=1,1,250][font=Times New Roman][size=3]ISP 1[/size][/font]
[font=Times New Roman][size=3]interface Loopback0[/size][/font]
[size=3][font=Times New Roman]
ip address 1.1.1.1 255.255.255.0[/font][/size]
[font=Times New Roman][size=3]![/size][/font]
[font=Times New Roman][size=3]interface Serial1/0[/size][/font]
[size=3][font=Times New Roman]
ip address 10.0.0.1 255.255.255.0[/font][/size]
[size=3][font=Times New Roman]
serial restart-delay 0[/font][/size]
[font=Times New Roman][size=3]![/size][/font]
[font=Times New Roman][size=3]![/size][/font]
[font=Times New Roman][size=3]router bgp 10[/size][/font]
[size=3][font=Times New Roman]
no synchronization[/font][/size]
[size=3][font=Times New Roman]
bgp log-neighbor-changes[/font][/size]
[size=3][font=Times New Roman]
network 1.1.1.0 mask 255.255.255.0[/font][/size]
[size=3][font=Times New Roman]
neighbor 10.0.0.2 remote-as 20[/font][/size]
[size=3][font=Times New Roman]
no auto-summary[/font][/size]
[font=Times New Roman][size=3]![/size][/font]
[/td][td=1,1,279][font=Times New Roman][size=3]ISP2[/size][/font]
[font=Times New Roman][size=3]interface Loopback0[/size][/font]
[size=3][font=Times New Roman]
ip address 3.3.3.3 255.255.255.0[/font][/size]
[font=Times New Roman][size=3]! [/size][/font]
[font=Times New Roman][size=3]interface Serial1/1[/size][/font]
[size=3][font=Times New Roman]
ip address 20.0.0.3 255.255.255.0[/font][/size]
[size=3][font=Times New Roman]
serial restart-delay 0[/font][/size]
[font=Times New Roman][size=3]![/size][/font]
[font=Times New Roman][size=3]router bgp 30[/size][/font]
[size=3][font=Times New Roman]
no synchronization[/font][/size]
[size=3][font=Times New Roman]
bgp log-neighbor-changes[/font][/size]
[size=3][font=Times New Roman]
network 3.3.3.0 mask 255.255.255.0[/font][/size]
[size=3][font=Times New Roman]
neighbor 20.0.0.2 remote-as 20[/font][/size]
[size=3][font=Times New Roman]
no auto-summary[/font][/size]
[/td][/tr][/table][/align][font=Times New Roman][size=3] [/size][/font]
[align=center][table=529][tr][td=1,1,529][font=Times New Roman][size=3]ITAA[/size][/font]
[font=Times New Roman][size=3]interface Loopback0[/size][/font]
[size=3][font=Times New Roman]
ip address 30.0.0.2 255.255.255.0[/font][/size]
[font=Times New Roman][size=3]![/size][/font]
[font=Times New Roman][size=3]interface Loopback1[/size][/font]
[size=3][font=Times New Roman]
ip address 30.0.1.2 255.255.255.0[/font][/size]
[font=Times New Roman][size=3]![/size][/font]
[font=Times New Roman][size=3]interface Serial1/0[/size][/font]
[size=3][font=Times New Roman]
ip address 20.0.0.2 255.255.255.0[/font][/size]
[size=3][font=Times New Roman]
serial restart-delay 0[/font][/size]
[font=Times New Roman][size=3]![/size][/font]
[font=Times New Roman][size=3]interface Serial1/1[/size][/font]
[size=3][font=Times New Roman]
ip address 10.0.0.2 255.255.255.0[/font][/size]
[size=3][font=Times New Roman]
serial restart-delay 0[/font][/size]
[font=Times New Roman][size=3]![/size][/font]
[font=Times New Roman][size=3]router bgp 20[/size][/font]
[size=3][font=Times New Roman]
no synchronization[/font][/size]
[size=3][font=Times New Roman]
bgp log-neighbor-changes[/font][/size]
[size=3][font=Times New Roman]
network 30.0.0.0 mask 255.255.255.0[/font][/size]
[size=3][font=Times New Roman]
network 30.0.1.0 mask 255.255.255.0[/font][/size]
[size=3][font=Times New Roman]
neighbor 10.0.0.1 remote-as 10[/font][/size]
[font=Times New Roman][size=3]neighbor 20.0.0.3 remote-as 30[/size][/font]
[size=3][font=Times New Roman]
no auto-summary[/font][/size]
[font=Times New Roman][size=3]![/size][/font]
[/td][/tr][/table][/align][size=3][font=宋体]安全配置：限制[/font][font=Times New Roman]ISP1 [/font][font=宋体]和[/font][font=Times New Roman] ISP 2[/font][font=宋体]互通[/font][/size]
[size=3][font=宋体]在[/font][font=Times New Roman]ITAA[/font][font=宋体]上配置访问控制链表，并在[/font][font=Times New Roman]BGP[/font][font=宋体]中使用[/font][font=Times New Roman]nei x.x.x.x distribute-list X [/font][font=宋体]命令控制路由的发布，以防止[/font][font=Times New Roman]ISP1[/font][font=宋体]和[/font][font=Times New Roman]ISP2[/font][font=宋体]互通。配置如下：[/font][/size]
[align=center][table=529][tr][td=1,1,568][font=Times New Roman][size=3]ITAA#conf t[/size][/font]
[font=Times New Roman][size=3]ITAA(config)# access-list 1 per 30.0.0.0 0.0.1.255[/size][/font]
[font=Times New Roman][size=3]ITAA(config)# router bgp 20[/size][/font]
[font=Times New Roman][size=3]ITAA(config-route)# nei 20.0.0.3 distribute-list 1 out[/size][/font]
[font=Times New Roman][size=3]ITAA(config-route)# nei 10.0.0.1 distribute-list 1 out[/size][/font]
[/td][/tr][/table][/align][size=3][font=宋体]在[/font][font=Times New Roman]ITAA[/font][font=宋体]上[/font][font=Times New Roman]clear ip bgp *[/font][font=宋体]重新建立[/font][font=Times New Roman]BGP[/font][font=宋体]连接之后，可以在[/font][font=Times New Roman]ISP1 [/font][font=宋体]和[/font][font=Times New Roman] ISP2 [/font][font=宋体]上分别查看[/font][font=Times New Roman]bgp[/font][font=宋体]信息：[/font][/size]
[font=Times New Roman][size=3] [/size][/font]
[align=center][table=529][tr][td=1,1,568][font=Times New Roman][size=3]ISP2#sh ip bgp[/size][/font]
[font=Times New Roman][size=3]BGP table version is 22, local router ID is 3.3.3.3[/size][/font]
[font=Times New Roman][size=3]Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,[/size][/font]
[size=3][font=Times New Roman]
r RIB-failure, S Stale[/font][/size]
[font=Times New Roman][size=3]Origin codes: i - IGP, e - EGP, ? - incomplete[/size][/font]
[font=Times New Roman][size=3] [/size][/font]
[size=3][font=Times New Roman]
Network
Next Hop
Metric LocPrf Weight Path[/font][/size]
[font=Times New Roman][size=3]*> 3.3.3.0/24
0.0.0.0
0
32768 i[/size][/font]
[font=Times New Roman][size=3]*> 30.0.0.0/24
20.0.0.2
0
0 20 i[/size][/font]
[font=Times New Roman][size=3]*> 30.0.1.0/24
20.0.0.2
0
0 20 i[/size][/font]
[/td][/tr][/table][/align][size=3][font=宋体]就无法看到[/font][font=Times New Roman]ISP1[/font][font=宋体]的路由信息了。[/font][/size]
[font=宋体][size=3]尝试方案：配置两条静态路由[/size][/font]
[font=Times New Roman][size=3] [/size][/font]
[align=center][table=529][tr][td=1,1,529][font=Times New Roman][size=3]ITAA(config)#ip route 0.0.0.0 0.0.0.0 10.0.0.1 210[/size][/font]
[font=Times New Roman][size=3]ITAA(config)#ip route 0.0.0.0 0.0.0.0 20.0.0.2 220[/size][/font]
[/td][/tr][/table][/align][font=Times New Roman][size=3] [/size][/font]
[align=center][table=529][tr][td=1,1,529][font=Times New Roman][size=3]ITAA#sh ip rou[/size][/font]
[color=red][size=3][font=Times New Roman]Gateway of last resort is 10.0.0.1 to network 0.0.0.0[/font][/size][/color]
[font=Times New Roman][size=3] [/size][/font]
[font=Times New Roman][size=3]B
210.210.210.0/24 [20/0] via 10.0.0.1, 00:56:26[/size][/font]
[size=3][font=Times New Roman]
1.0.0.0/24 is subnetted, 1 subnets[/font][/size]
[font=Times New Roman][size=3]B
1.1.1.0 [20/0] via 10.0.0.1, 00:56:26[/size][/font]
[size=3][font=Times New Roman]
3.0.0.0/24 is subnetted, 1 subnets[/font][/size]
[font=Times New Roman][size=3]B
3.3.3.0 [20/0] via 20.0.0.3, 01:25:08[/size][/font]
[size=3][font=Times New Roman]
20.0.0.0/24 is subnetted, 1 subnets[/font][/size]
[font=Times New Roman][size=3]C
20.0.0.0 is directly connected, Serial1/0[/size][/font]
[size=3][font=Times New Roman]
10.0.0.0/24 is subnetted, 1 subnets[/font][/size]
[font=Times New Roman][size=3]C
10.0.0.0 is directly connected, Serial1/1[/size][/font]
[size=3][font=Times New Roman]
30.0.0.0/24 is subnetted, 2 subnets[/font][/size]
[font=Times New Roman][size=3]C
30.0.0.0 is directly connected, Loopback0[/size][/font]
[font=Times New Roman][size=3]C
30.0.1.0 is directly connected, Loopback1[/size][/font]
[color=red][size=3][font=Times New Roman]S*
0.0.0.0/0 [210/0] via 10.0.0.1[/font][/size][/color]
[font=Times New Roman][size=3] [/size][/font]
[/td][/tr][/table][/align][font=Times New Roman][size=3] [/size][/font]
[size=3][font=宋体]这么看起来，貌似没有什么问题，最后的[/font][font=Times New Roman]resort[/font][font=宋体]也成功的设置成为[/font][font=Times New Roman]10.0.0.1[/font][font=宋体]，但是，如果这条链路断开，会不会马上切换到另一条静态路由呢？我们来看一下：[/font][/size]
[size=3][font=宋体]首先，在[/font][font=Times New Roman]ISP1[/font][font=宋体]上[/font][font=Times New Roman]shutdown[/font][font=宋体]掉[/font][font=Times New Roman]s1/0[/font][font=宋体]端口，在[/font][font=Times New Roman]ITAA[/font][font=宋体]上观看现象很明显：[/font][/size]
[align=center][table=529][tr][td=1,1,568][font=Times New Roman][size=3]ITAA#sh ip rou[/size][/font]
[font=Times New Roman][size=3]Codes: C - connected, S - static, R - RIP, M - mobile, B - BGP[/size][/font]
[size=3][font=Times New Roman]
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area [/font][/size]
[size=3][font=Times New Roman]
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2[/font][/size]
[size=3][font=Times New Roman]
E1 - OSPF external type 1, E2 - OSPF external type 2[/font][/size]
[size=3][font=Times New Roman]
i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2[/font][/size]
[size=3][font=Times New Roman]
ia - IS-IS inter area, * - candidate default, U - per-user static route[/font][/size]
[size=3][font=Times New Roman]
o - ODR, P - periodic downloaded static route[/font][/size]
[font=Times New Roman][size=3] [/size][/font]
[font=Times New Roman][size=3]Gateway of last resort is 10.0.0.1 to network 0.0.0.0[/size][/font]
[font=Times New Roman][size=3] [/size][/font]
[font=Times New Roman][size=3]B
210.210.210.0/24 [20/0] via 10.0.0.1, 01:00:11[/size][/font]
[size=3][font=Times New Roman]
1.0.0.0/24 is subnetted, 1 subnets[/font][/size]
[font=Times New Roman][size=3]B
1.1.1.0 [20/0] via 10.0.0.1, 01:00:11[/size][/font]
[size=3][font=Times New Roman]
3.0.0.0/24 is subnetted, 1 subnets[/font][/size]
[font=Times New Roman][size=3]B
3.3.3.0 [20/0] via 20.0.0.3, 01:28:53[/size][/font]
[size=3][font=Times New Roman]
20.0.0.0/24 is subnetted, 1 subnets [/font][/size]
[font=Times New Roman][size=3]C
20.0.0.0 is directly connected, Serial1/0[/size][/font]
[size=3][font=Times New Roman]
10.0.0.0/24 is subnetted, 1 subnets[/font][/size]
[font=Times New Roman][size=3]C
10.0.0.0 is directly connected, Serial1/1[/size][/font]
[size=3][font=Times New Roman]
30.0.0.0/24 is subnetted, 2 subnets[/font][/size]
[font=Times New Roman][size=3]C
30.0.0.0 is directly connected, Loopback0[/size][/font]
[font=Times New Roman][size=3]C
30.0.1.0 is directly connected, Loopback1[/size][/font]
[font=Times New Roman][size=3]S*
0.0.0.0/0 [210/0] via 10.0.0.1
…………………………………….[/size][/font][font=宋体][size=18pt]①[/size][/font]
[font=Times New Roman][size=3]ITAA#p 1.1.1.1[/size][/font]
[font=Times New Roman][size=3]Type escape sequence to abort.[/size][/font]
[font=Times New Roman][size=3]Sending 5, 100-byte ICMP Echos to 1.1.1.1, timeout is 2 seconds:[/size][/font]
[font=Times New Roman][size=3].....[/size][/font]
[font=Times New Roman][size=3]Success rate is 0 percent (0/5)………………………………………………[/size][/font][font=宋体][size=18pt]②[/size][/font]
[font=Times New Roman][size=3]ITAA#[/size][/font]
[font=Times New Roman][size=3]*Apr
4 12:15:24.871: %LINEPROTO-5-UPDOWN: Line protocol on Interface Serial1/1, changed state to down[/size][/font][font=宋体][size=18pt]③[/size][/font]
[font=Times New Roman][size=3]*Apr
4 12:15:24.883: %BGP-5-ADJCHANGE: neighbor 10.0.0.1 Down Interface flap[/size][/font]
[font=Times New Roman][size=3]ITAA#sh ip rou[/size][/font]
[font=Times New Roman][size=3]Gateway of last resort is 20.0.0.3 to network 0.0.0.0[/size][/font]
[font=Times New Roman][size=3] [/size][/font]
[size=3][font=Times New Roman]
3.0.0.0/24 is subnetted, 1 subnets[/font][/size]
[font=Times New Roman][size=3]B
3.3.3.0 [20/0] via 20.0.0.3, 01:34:39[/size][/font]
[size=3][font=Times New Roman]
20.0.0.0/24 is subnetted, 1 subnets[/font][/size]
[font=Times New Roman][size=3]C
20.0.0.0 is directly connected, Serial1/0[/size][/font]
[size=3][font=Times New Roman]
30.0.0.0/24 is subnetted, 2 subnets[/font][/size]
[font=Times New Roman][size=3]C
30.0.0.0 is directly connected, Loopback0[/size][/font]
[font=Times New Roman][size=3]C
30.0.1.0 is directly connected, Loopback1[/size][/font]
[font=Times New Roman][size=3]S*
0.0.0.0/0 [220/0] via 20.0.0.3…………………………………………..[/size][/font][font=宋体][size=18pt]④[/size][/font]
[/td][/tr][/table][/align][font=Times New Roman][size=3] [/size][/font]
[size=3][font=宋体]上面的表格是在我们[/font][font=Times New Roman]shutdown
ISP1[/font][font=宋体]对应端口后的现象，我们很明显的看到，三个序号的顺序很不正常，首先路由表中有通往[/font][font=Times New Roman]1.1.1.1[/font][font=宋体]的路由，但却又无法[/font][font=Times New Roman]ping[/font][font=宋体]通，然后才收到[/font][font=Times New Roman]BGP[/font][font=宋体]链路[/font][font=Times New Roman]down[/font][font=宋体]掉的信息，其次才是路由表的更新，这样的做法会导致一定时间[/font][font=Times New Roman]ITAA[/font][font=宋体]无法访问非洲互联网，情况极其不能接受！怎么办？改！[/font][/size]
[font=宋体][size=3]最终方案：配置默认路由，再配一条静态路由[/size][/font]
[size=3][font=Times New Roman] [/font][font=宋体]我们只好采用默认路由方式一试！[/font][/size]
[size=3][font=Times New Roman] [/font][font=宋体]首先，我们在[/font][font=Times New Roman]ISP1[/font][font=宋体]中再起一个环回口[/font][font=Times New Roman],IP[/font][font=宋体]为[/font][font=Times New Roman]210.210.210.1[/font][font=宋体]，并在[/font][font=Times New Roman]BGP[/font][font=宋体]通告出来。[/font][/size]
[align=center][table=529][tr][td=1,1,568][font=Times New Roman][size=3]ITAA#sh ip bgp[/size][/font]
[size=3][font=Times New Roman]
Network
Next Hop
Metric LocPrf Weight Path[/font][/size]
[font=Times New Roman][size=3]*> 1.1.1.0/24
10.0.0.1
0
0 10 i[/size][/font]
[font=Times New Roman][size=3]*> 3.3.3.0/24
20.0.0.3
0
0 30 i[/size][/font]
[font=Times New Roman][size=3]*> 30.0.0.0/24
0.0.0.0
0
32768 i[/size][/font]
[font=Times New Roman][size=3]*> 30.0.1.0/24
0.0.0.0
0
32768 i[/size][/font]
[font=Times New Roman][size=3]*> 210.210.210.0
10.0.0.1
0
0 10 i[/size][/font]
[/td][/tr][/table][/align][size=3][font=Times New Roman] [/font][font=宋体]在[/font][font=Times New Roman]ITAA[/font][font=宋体]中配置：[/font][font=Times New Roman]ip default-network 210.210.210.0[/font][font=宋体]，查看路由表[/font][font=Times New Roman]:[/font][/size]
[align=center][table=529][tr][td=1,1,568][font=Times New Roman][size=3]ITAA#sh ip rou[/size][/font]
[color=red][size=3][font=Times New Roman]Gateway of last resort is 10.0.0.1 to network 210.210.210.0[/font][/size][/color]
[font=Times New Roman][size=3] [/size][/font]
[color=red][size=3][font=Times New Roman]B*
210.210.210.0/24 [20/0] via 10.0.0.1, 00:01:08[/font][/size][/color]
[size=3][font=Times New Roman]
1.0.0.0/24 is subnetted, 1 subnets[/font][/size]
[font=Times New Roman][size=3]B
1.1.1.0 [20/0] via 10.0.0.1, 00:01:08[/size][/font]
[size=3][font=Times New Roman]
3.0.0.0/24 is subnetted, 1 subnets[/font][/size]
[font=Times New Roman][size=3]B
3.3.3.0 [20/0] via 20.0.0.3, 01:39:21[/size][/font]
[size=3][font=Times New Roman]
20.0.0.0/24 is subnetted, 1 subnets[/font][/size]
[font=Times New Roman][size=3]C
20.0.0.0 is directly connected, Serial1/0[/size][/font]
[size=3][font=Times New Roman]
10.0.0.0/24 is subnetted, 1 subnets[/font][/size]
[font=Times New Roman][size=3]C
10.0.0.0 is directly connected, Serial1/1[/size][/font]
[size=3][font=Times New Roman]
30.0.0.0/24 is subnetted, 2 subnets[/font][/size]
[font=Times New Roman][size=3]C
30.0.0.0 is directly connected, Loopback0[/size][/font]
[font=Times New Roman][size=3]C
30.0.1.0 is directly connected, Loopback1[/size][/font]
[color=red][size=3][font=Times New Roman]S*
0.0.0.0/0 [220/0] via 20.0.0.3[/font][/size][/color]
[/td][/tr][/table][/align][font=Times New Roman][size=3] [/size][/font]
[size=3][font=Times New Roman]OK,[/font][font=宋体]到此我们看到了一个比较不错的结果，路由表里面同时存在两条[/font][font=Times New Roman]”*”[/font][font=宋体]路由，可以实现无间断的路由，我们来验证一下，在[/font][font=Times New Roman]ISP1[/font][font=宋体]上关闭接口，当我们迅速切回到[/font][font=Times New Roman]ITAA[/font][font=宋体]上查看路由信息的时候，依然没有及时更新路由，但是没关系，[/font][color=red][font=Times New Roman]S*
0.0.0.0/0 [220/0] via 20.0.0.3[/font][/color][color=red][font=宋体]，[/font][/color][font=宋体]这条路由不是吃素的，可以迅速为我们接通非洲互联网！[/font][/size]
[font=宋体][size=3]结论：[/size][/font]
[size=3][font=Times New Roman] [/font][font=宋体]想要无间断的路由，首先我们不能强迫[/font][font=Times New Roman]BGP[/font][font=宋体]的反应时间，我们没有办法，所以我们就要想办法在路由表中安置两条路由，那么我们的方案就是使用[/font][font=Times New Roman]ip default-net [/font][font=宋体]命令！[/font][/size]
[size=3][font=Times New Roman] [/font][font=宋体]特别注意：在[/font][font=Times New Roman]BGP[/font][font=宋体]中，[/font][font=Times New Roman]network[/font][font=宋体]命令必须是路由条目里面的，包括后面的掩码都非常重要，这点可能大家都知道，但往往容易出错，导致[/font][font=Times New Roman]BGP[/font][font=宋体]中发布路由不成功[/font][font=Times New Roman];[/font][/size]
[font=宋体][size=3]一些未解疑问：[/size][/font]
[font=Times New Roman][size=3] [/size][/font]
[table][tr][td=1,1,568][size=3][font=宋体]在设置[/font][font=Times New Roman]default-network[/font][font=宋体]的时候也得注意掩码，应该是主类地址，但有个疑问，当我设置为[/font][font=Times New Roman]5.0.0.0[/font][font=宋体]这样的[/font][font=Times New Roman]A[/font][font=宋体]类地址的时候，在[/font][font=Times New Roman]sh ip rou[/font][font=宋体]的时候，[/font][font=Times New Roman] [/font][font=宋体]显示[/font][font=Times New Roman]Gateway of last resort is not set.[/font][font=宋体]但在路由条目中[/font][font=Times New Roman]5.0.0.0/24[/font][font=宋体]这条前面会有一个[/font][font=Times New Roman]"*",[/font][font=宋体]表示是制定的默认路由，而设置为类似[/font][font=Times New Roman]210.210.210.0[/font][font=宋体]这样的[/font][font=Times New Roman]C[/font][font=宋体]类地址的时候就可以显示[/font][/size]
[size=3][font=Times New Roman]Gateway of last resort is 10.0.0.1 to network 210.210.210.0[/font][font=宋体]，下面对应的路由条目也有[/font][font=Times New Roman]"*";[/font][/size]
[font=宋体][size=3]为什么？[/size][/font]
[/td][/tr][/table]
