I’m a little embarrassed to be asking this but here goes.
In a training video for CCENT, I see a switch connected to 2 PCs that are pinging each other on the same subnet. I try to replicate the setup with 2 Linux PCs and the PCs cannot ping each other.
After quite a bit of diagnosing I come up with the reason that they are not pinging each other, is because initially PC1 does not know PC2’s MAC address and because the switch is a Layer 2 device, it cannot forward the frame. Once I add a router to the topology and tell the PCs to use it as the default gateway, the PCs can reach each other.
My question is, are my assumptions correct? or is there a way to configure either my L2 switch (Cisco 2960) or my PCs to ping each other without an additional router? I am really curious to know how the instructor did it in the video, but at this point can only surmise that the Windows PCs he is using are helping with the ARP somehow that my Linux PC doesn’t.
Edit: adding configs
Switch#show vlan
VLAN Name Status Ports
---- -------------------------------- --------- -------------------------------
1 default active Fa0/1, Fa0/2, Fa0/3, Fa0/4
Fa0/5, Fa0/6, Fa0/7, Fa0/8
Fa0/9, Fa0/10, Fa0/11, Fa0/12
Fa0/13, Fa0/14, Fa0/15, Fa0/16
Fa0/17, Fa0/18, Fa0/19, Fa0/20
Fa0/21, Fa0/22, Fa0/23, Fa0/24
1002 fddi-default act/unsup
1003 token-ring-default act/unsup
1004 fddinet-default act/unsup
1005 trnet-default act/unsup
VLAN Type SAID MTU Parent RingNo BridgeNo Stp BrdgMode Trans1 Trans2
---- ----- ---------- ----- ------ ------ -------- ---- -------- ------ ------
1 enet 100001 1500 - - - - - 0 0
1002 fddi 101002 1500 - - - - - 0 0
1003 tr 101003 1500 - - - - - 0 0
1004 fdnet 101004 1500 - - - ieee - 0 0
1005 trnet 101005 1500 - - - ibm - 0 0
Primary Secondary Type Ports
------- --------- ----------------- ------------------------------------------
Switch#show ip int brief
Interface IP-Address OK? Method Status Protocol
Vlan1 10.3.1.1 YES NVRAM up up
FastEthernet0/1 unassigned YES unset up up
FastEthernet0/2 unassigned YES unset down down
FastEthernet0/3 unassigned YES unset down down
FastEthernet0/4 unassigned YES unset down down
FastEthernet0/5 unassigned YES unset down down
FastEthernet0/6 unassigned YES unset down down
FastEthernet0/7 unassigned YES unset down down
FastEthernet0/8 unassigned YES unset down down
FastEthernet0/9 unassigned YES unset down down
FastEthernet0/10 unassigned YES unset down down
FastEthernet0/11 unassigned YES unset down down
FastEthernet0/12 unassigned YES unset down down
FastEthernet0/13 unassigned YES unset down down
FastEthernet0/14 unassigned YES unset down down
FastEthernet0/15 unassigned YES unset down down
FastEthernet0/16 unassigned YES unset down down
FastEthernet0/17 unassigned YES unset down down
FastEthernet0/18 unassigned YES unset down down
FastEthernet0/19 unassigned YES unset down down
FastEthernet0/20 unassigned YES unset down down
Switch#show int vlan 1
Vlan1 is up, line protocol is up
Hardware is EtherSVI, address is 0025.8347.d4c0 (bia 0025.8347.d4c0)
Internet address is 10.3.1.1/24
MTU 1500 bytes, BW 1000000 Kbit/sec, DLY 10 usec,
reliability 255/255, txload 1/255, rxload 1/255
Encapsulation ARPA, loopback not set
Keepalive not supported
ARP type: ARPA, ARP Timeout 04:00:00
Last input 00:00:01, output 03:07:32, output hang never
Last clearing of "show interface" counters never
Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0
Queueing strategy: fifo
Output queue: 0/40 (size/max)
5 minute input rate 0 bits/sec, 0 packets/sec
5 minute output rate 0 bits/sec, 0 packets/sec
7073 packets input, 586827 bytes, 0 no buffer
Received 0 broadcasts (0 IP multicasts)
0 runts, 0 giants, 0 throttles
0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored
1 packets output, 64 bytes, 0 underruns
0 output errors, 2 interface resets
0 unknown protocol drops
0 output buffer failures, 0 output buffers swapped out
Switch#
And Linux PC
bob bob # ip addr
1: lo: mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1
link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
inet 127.0.0.1/8 scope host lo
valid_lft forever preferred_lft forever
inet6 ::1/128 scope host
valid_lft forever preferred_lft forever
2: enp9s0: mtu 1500 qdisc mq state UP group default qlen 1000
link/ether 00:21:70:b7:c6:9c brd ff:ff:ff:ff:ff:ff
inet 10.3.1.50/32 scope global enp9s0
valid_lft forever preferred_lft forever
inet6 fe80::221:70ff:feb7:c69c/64 scope link
valid_lft forever preferred_lft forever
3: wlan0: mtu 1500 qdisc noop state DOWN group default qlen 1000
link/ether 00:22:5f:1e:4e:e6 brd ff:ff:ff:ff:ff:ff
bob bob #
running-config
Switch#show run
Building configuration...
Current configuration : 2855 bytes
!
version 15.0
no service pad
service timestamps debug datetime msec
service timestamps log datetime msec
no service password-encryption
!
hostname Switch
!
boot-start-marker
boot-end-marker
!
!
no aaa new-model
system mtu routing 1500
!
!
!
!
crypto pki trustpoint TP-self-signed-2202522752
enrollment selfsigned
subject-name cn=IOS-Self-Signed-Certificate-2202522752
revocation-check none
rsakeypair TP-self-signed-2202522752
!
!
crypto pki certificate chain TP-self-signed-2202522752
certificate self-signed 01
3082022B 30820194 A0030201 02020101 300D0609 2A864886 F70D0101 05050030
31312F30 2D060355 04031326 494F532D 53656C66 2D536967 6E65642D 43657274
69666963 6174652D 32323032 35323237 3532301E 170D3933 30333031 30303031
30365A17 0D323030 31303130 30303030 305A3031 312F302D 06035504 03132649
4F532D53 656C662D 5369676E 65642D43 65727469 66696361 74652D32 32303235
32323735 3230819F 300D0609 2A864886 F70D0101 01050003 818D0030 81890281
8100E4DB 6BDBD2DC 37055DFA 282999AE B96FC640 2241FF8A 430ED5FF A6017E03
F6B19437 AA7BE507 13CE0C75 679C17C0 32FBE9E3 7AD23E1B 25BEEF58 73A2C55F
A7156C6A ECCF31EF 537EC8AC 596AB7A5 71C29EEA 217D8DE4 95B8D7F1 47FF5381
986C93D6 D82C6734 1DE12C83 770EA60B 498A8D75 B9A1AAC6 A999B598 1E5E3081
C1530203 010001A3 53305130 0F060355 1D130101 FF040530 030101FF 301F0603
551D2304 18301680 141B3F0D 0506EF36 1F18AC79 78C722FD 82ADC5A4 BA301D06
03551D0E 04160414 1B3F0D05 06EF361F 18AC7978 C722FD82 ADC5A4BA 300D0609
2A864886 F70D0101 05050003 8181000A E3F3216C 34E27078 0FD09863 A1FC8958
EA67A0E9 0B1B26F4 CC675FEC 4C43B23A AA3CB113 973BD666 F5DFF4E9 B5C6372F
C1D0B75F CFF7EEA4 CBCBE18E A633BB8A B59841BC 4711FE62 945A1276 0CD80044
F0D34DDD BA3B346B EC97238C 479D686F 9EC88F50 9A5E786F D8DD023D 5142C4D1
3EED7955 AFBB2A10 DF839E02 0CE192
quit
!
!
!
!
!
spanning-tree mode pvst
spanning-tree extend system-id
!
vlan internal allocation policy ascending
!
!
!
!
!
interface FastEthernet0/1
!
interface FastEthernet0/2
!
interface FastEthernet0/3
!
interface FastEthernet0/4
!
interface FastEthernet0/5
!
interface FastEthernet0/6
!
interface FastEthernet0/7
!
interface FastEthernet0/8
!
interface FastEthernet0/9
!
interface FastEthernet0/10
!
interface FastEthernet0/11
!
interface FastEthernet0/12
!
interface FastEthernet0/13
!
interface FastEthernet0/14
!
interface FastEthernet0/15
!
interface FastEthernet0/16
!
interface FastEthernet0/17
!
interface FastEthernet0/18
!
interface FastEthernet0/19
!
interface FastEthernet0/20
!
interface FastEthernet0/21
!
interface FastEthernet0/22
!
interface FastEthernet0/23
!
interface FastEthernet0/24
!
interface Vlan1
ip address 10.3.1.1 255.255.255.0
no ip route-cache
!
ip http server
ip http secure-server
!
!
line con 0
exec-timeout 0 0
logging synchronous
line vty 0 4
login
line vty 5 15
login
!
end
Switch#
Best Answer
The problem is with this:
Because you didn't specify a network mask, the address was given a host-only /32 (255.255.255.255) mask. No other hosts belong to the network, therefore any attempts to ping an address will fail (check
ip routeto verify.)The reason why
ip route add 10.3.1.51worked (from your answer) is because you added another host-only route, so your routes are this now:Only these two addresses (and the loopback addresses) will work because they're the only ones that you have said exist!
You'll need both hosts to share a common network, or have some sort of route between them, before they will be able to see each other. In this case, try