网络工程 - 电缆调制解调器 ARP 行为 - 吾爱随笔录

我在一个非常简单的拓扑结构中有三个第 3 层设备：

PC1 -> [Fe0/0] C2621 [Fe0/1] -> [Fe0/2] Modem [WAN] -> Internet


PC1:   192.168.254.100/24


C2621: Fe0/0: 192.168.254.254/24
       Fe0/1: 10.0.0.3/24


Modem: Fe0/2: 10.0.0.1/24

从 PC1 我可以 ping 调制解调器：

Ping statistics for 10.0.0.1:
Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),
Approximate round trip times in milli-seconds:
Minimum = 0ms, Maximum = 1ms, Average = 0ms

调制解调器没有分配任何静态路由。ping 怎么可能通过？我在 GNS3 中使用三个具有完全相同 IP 地址的路由器创建了相同的拓扑，但无法 ping 调制解调器：

R3#ping 10.0.0.1
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 10.0.0.1, timeout is 2 seconds:
.....
Success rate is 0 percent (0/5)

这种型号的调制解调器不允许我查看 ARP 表。此外，traceroute 显示 ping 转到 10.1.1.1，然后转到 10.0.0.1。正如它应该的那样，如果调制解调器实际上有一条返回 10.1.1.0/24 网络的路由，但它没有。我什至尝试断开从 R1 到调制解调器的电缆，以查看 ping 是否会失败。他们做到了。

调制解调器知道 10.1.1.0/24 网络在哪里完全没有意义。这怎么可能？调制解调器是 SBG6580 电缆调制解调器

附加信息：`

C2621#show ip rou
Codes: C - connected, S - static, R - RIP, M - mobile, B - BGP
       D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
       N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
       E1 - OSPF external type 1, E2 - OSPF external type 2
       i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
       ia - IS-IS inter area, * - candidate default, U - per-user static route
       o - ODR, P - periodic downloaded static route

Gateway of last resort is not set

     10.0.0.0/24 is subnetted, 1 subnets
C       10.0.0.0 is directly connected, FastEthernet0/1
C    192.168.254.0/24 is directly connected, FastEthernet0/0.254




C2621#show run
Building configuration...

Current configuration : 1109 bytes
!
version 12.3
service timestamps debug datetime msec
service timestamps log datetime msec
no service password-encryption
!
hostname C2621
!
boot-start-marker
boot-end-marker
!
enable secret 5 $1$sc4H$NGsbRnN8X2zErueSVyaim/
!
no aaa new-model
ip subnet-zero
ip cef
!
!
!
no ip domain lookup
!
!
!
!
!    
!
!
!
!
!
!
!
!
!
!
interface FastEthernet0/0
 no ip address
 duplex auto
 speed auto
!
interface FastEthernet0/0.254
 encapsulation dot1Q 1 native
 ip address 192.168.254.254 255.255.255.0
 no snmp trap link-status
!
interface Serial0/0
 no ip address
 shutdown
 no fair-queue
!
interface FastEthernet0/1
 description Test Description
 ip address 10.0.0.3 255.255.255.0
 no ip proxy-arp
 duplex auto
 speed auto
!
ip classless
ip http server
!
!
!
voice-port 1/0/0
!
voice-port 1/0/1
!
voice-port 1/1/0
!
voice-port 1/1/1
!
!
!
!
!
!
line con 0
logging synchronous
line aux 0
line vty 0 1
 exec-timeout 0 0
 password cisco
 login
 transport input telnet
line vty 2 4
 exec-timeout 0 0
 password cisco
 login
line vty 5
 exec-timeout 0 0
 password cisco
 login
line vty 6 15
 password cisco
 login
!
!
end






C2621#show ip arp
Protocol  Address          Age (min)  Hardware Addr   Type   Interface
Internet  10.0.0.3                -   0001.9651.dea1  ARPA   FastEthernet0/1
Internet  10.0.0.1                2   94cc.b902.7976  ARPA   FastEthernet0/1
Internet  192.168.254.254         -   0001.9651.dea0  ARPA   FastEthernet0/0.254
Internet  192.168.254.4          11   0017.5a57.3480  ARPA   FastEthernet0/0.254
Internet  192.168.254.2          11   0011.bb6d.0300  ARPA   FastEthernet0/0.254
Internet  192.168.254.3          11   0015.f9f8.0900  ARPA   FastEthernet0/0.254
Internet  192.168.254.1          11   0017.59eb.3580  ARPA   FastEthernet0/0.254
Internet  192.168.254.100         2   e000.0000.129c  ARPA   FastEthernet0/0.254


C2621#show version
Cisco Internetwork Operating System Software
IOS (tm) C2600 Software (C2600-IPVOICE-M), Version 12.3(15), RELEASE SOFTWARE (fc3)
Technical Support: http://www.cisco.com/techsupport
Copyright (c) 1986-2005 by cisco Systems, Inc.
Compiled Tue 24-May-05 14:01 by ssearch
Image text-base: 0x80008098, data-base: 0x8183E8D4

ROM: System Bootstrap, Version 11.3(2)XA4, RELEASE SOFTWARE (fc1)
ROM: C2600 Software (C2600-IPVOICE-M), Version 12.3(15), RELEASE SOFTWARE (fc3)

C2621 uptime is 3 hours, 29 minutes
System returned to ROM by power-on
System image file is "flash:c2600-ipvoice-mz.123-15.bin"

cisco 2621 (MPC860) processor (revision 0x102) with 61440K/4096K bytes of memory.
Processor board ID JAB04130AL8 (912529492)
M860 processor: part number 0, mask 49
Bridging software.
X.25 software, Version 3.0.0.
2 FastEthernet/IEEE 802.3 interface(s)
1 Serial network interface(s)
2 Voice FXO interface(s)
2 Voice FXS interface(s)
32K bytes of non-volatile configuration memory.
16384K bytes of processor board System flash (Read/Write)

Configuration register is 0x2102