Interesting phenomenon of pinging the IP address of the local port on the vro

(The Frame Relay mentioned below is point-to-point, which is different from point-to-point)

 

When you ping the IP address of a local machine on a computer, the IP address is only sent back to the computer and not to the network. However, the IP address on the router is different.

 

The s1/0 port IP address on R1 is 1.1.1.1 The S1/0 port IP address on R2 is 1.1.1.2

Now we need to capture packets on the S1/0 port of R2...

1. ping 1.1.1.2 ICMP packets on R1 are caught normally, and everything is normal as we think.

2. ping 1.1.1.1 on R1. The result is different from what we think. Please refer:

 

Five ping packets are sent on router R1, and 20 ping packets are captured on router R2. That is to say, when R1 ping the IP address on its own port, it first sends a request packet to R2, then R2 forwards it to R1, R1 sends a reply packet to R2, and R2 forwards it to R1.
 
 
 
Now let's take a look at the RTT (round trip time) displayed after the previous ping on R1)
 
R1 # ping 1.1.1.1
 
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 1.1.1.1, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 108/200/272 MS
R1 # ping 1.1.1.2
 
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 1.1.1.2, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 60/126/184 MS
 
The RTT value when pinging R2.
 
 
 
 
 
Traceroute 1.1.1.1 on R1:
 
R1 # traceroute 1.1.1.1
 
Type escape sequence to abort.
Tracing the route to 1.1.1.1
 
1 1.1.1.2 256 msec 108 msec 160 msec
2 1.1.1.1 216 msec * 224 msec
 
This makes it easy to see the path of the ICMP packet.
 
 
 
So, is this possible for any two directly connected vro ports? The answer is no.
 
When the serial port of the two routers is changed to the Fast Ethernet port, the packets sent from R1 to the IP address of the local port are not sent, but the local loopback is used.
 
 
 
Why? Please show the ip route yourself.
 
 
 
This article is from Xin-lu-li-cheng "blog