Why can we ping the ip address from ProxySG even through the physical interface is down?
Article ID: 167506
Updated On:
Products
Issue/Introduction
We can ping the IP address from the ProxySG CLI even through the interface is physically down.
From below, we find the interface of 1:0 and 1:1 are down. Interface 0:0 is up, and configured with different IP address than 1:0 and 1:1.
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16.176#show inter all
Ethernet interface 0:0
Internet address: 10.254.16.188 netmask 255.255.255.0
Internet address: fe80::2d0:83ff:fe05:9635 prefixlen 64
MTU size: 1500
Link status: autosensed to full duplex, 1 gigabit/sec network
Reject inbound: disabled
Allow intercept: enabled
VLAN trunk: enabled
Native VLAN: 1
Spanning tree: disabled
IPv6 auto-linklocal: enabled
Member of the bridge: none
Ethernet interface 1:0 (WAN)
Internet address: 10.254.16.176 netmask 255.255.255.0
Internet address: fe80::2d0:83ff:fe05:9636 prefixlen 64
MTU size: 1500
Link status: no link
Reject inbound: disabled
Allow intercept: enabled
VLAN trunk: enabled
Native VLAN: 1
Spanning tree: disabled
IPv6 auto-linklocal: enabled
Member of the bridge: passthru-1
Ethernet interface 1:1 (LAN)
Internet address: 10.254.15.111 netmask 255.255.255.0
Internet address: fe80::2d0:83ff:fe05:9637 prefixlen 64
MTU size: 1500
Link status: no link
Reject inbound: disabled
Allow intercept: enabled
VLAN trunk: enabled
Native VLAN: 1
Spanning tree: disabled
IPv6 auto-linklocal: enabled
Member of the bridge: passthru-1
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But we still can ping the IP addresses of interface 1:0 and 1:1 from the ProxySG CLI, as shown next.
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16.176#ping 10.254.16.176
PING 10.254.16.176 (10.254.16.176): 56 data bytes
64 bytes from 10.254.16.176: icmp_seq=0 ttl=64 time=0.094 ms
64 bytes from 10.254.16.176: icmp_seq=1 ttl=64 time=0.055 ms
--- 10.254.16.176 ping statistics ---
2 packets transmitted, 2 packets received, 0% packet loss
round-trip min/avg/max/stddev = 0.055/0.074/0.094/0.020 ms
16.176#
16.176#ping 10.254.15.111
PING 10.254.15.111 (10.254.15.111): 56 data bytes
64 bytes from 10.254.15.111: icmp_seq=0 ttl=64 time=0.072 ms
64 bytes from 10.254.15.111: icmp_seq=1 ttl=64 time=0.044 ms
--- 10.254.15.111 ping statistics ---
2 packets transmitted, 2 packets received, 0% packet loss
round-trip min/avg/max/stddev = 0.044/0.058/0.072/0.014 ms
16.176#
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Resolution
This happens because the IP addresses of interface 1:0 and 1:1 are fixed in the ProxySG appliance when we configured the ProxySG.
We can see from the output of the ARP and IP Route Table belowbelow that the interface following the interface 1:0 and 1:1 IP address is Loopback. Loopback is always up, so we can always ping these two IP addresses from the ProxySG.
We don't successfully ping the two IP addresses from outside when they are physically down.
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16.176#show arp
; TCP/IP Statistics
TCP/IP ARP Information
IP Address MAC Address Interface
10.254.15.111 00:d0:83:05:96:37 passthru-1 permanent
10.254.16.1 00:23:9c:21:16:cb 0:0
10.254.16.115 f0:de:f1:29:d5:36 0:0
10.254.16.176 00:d0:83:05:96:35 0:0 permanent
10.254.16.188 00:d0:83:05:96:35 0:0 permanent
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16.176#show ip-route-table
; TCP/IP Routing Table
Routing tables
Internet:
Destination Gateway Flags Refs Use Netif Expire
default 10.254.16.1 UGS 15 4625 0:0
10.254.15.0/24 link#3 UC 0 4 1:1
10.254.15.111 00:d0:83:05:96:37 UHLW 0 4 loopback -----> the next interface is loopback
10.254.16.0/24 link#2 UC 0 7 0:0 =>
10.254.16.0/24 link#4 UC 0 0 1:0
10.254.16.1 00:23:9c:21:16:cb UHLW 1 2 0:0 111
10.254.16.115 f0:de:f1:29:d5:36 UHLW 0 570 0:0 717
10.254.16.176 00:d0:83:05:96:35 UHLW 0 3 loopback
10.254.16.188 00:d0:83:05:96:35 UHLW 0 7 loopback -----> the next interface is loopback
127.0.0.1 127.0.0.1 UH 2 3709 loopback
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