Interface gets pinged even when cable not connected

Derelict

Do it again, ping, look at the ARP table, get the MAC address for the IP you're magically pinging and track it down.

Is there Wi-Fi involved anywhere?

johnpoz

Think about it for all of 2 seconds dude… If you have something connected with a wire with no other paths to it.. And you can still ping that IP.. you either have another path to that IP.. Or your pinging something else that answers to that IP..

Or by some crazy odd weird magic your packets are jumping the air gap and flowing through the air??

What is more logical your over looking a path or pinging something else with that same ip??? My vote is your over looking something... Come on... packets don't magically flow over the air gap...

Just think about it for 2 freaking seconds... That you even posted this thread points to your high on something or not thinking straight or just some lame attempt at trolling.

bhawk6901

Since nobody believes me yet, i'm posting a diagram what I am doing now to clarify things.
Eth0 ip: 192.168.1.1/24
PC1 ip: 192.168.1.10/24
Eth1 ip: 192.168.2.1/24
PC2 ip: 192.168.2.10/24

Disconnected the cable between Eth0 & PC1
Ping Eth0 from PC2 and it gets pinged

Untitled.png_thumb

Derelict

pfSense does not take interface IP addresses down when ethernet carrier is lost like, say, a Cisco does.

In fact, the interface addresses actually route to loopback interfaces internally.

What you're seeing is completely normal. You can ping a local interface address even though the interface has nothing plugged into it. Your initial description had everyone thinking you were saying you could still ping 192.168.1.1 from 192.168.1.10 even though it was unplugged.

Amazing how a diagram clears things up immediately.

Supermule

HAHAHAHAHAHAHAHAH

You gotta be kidding :D

Your pinging the interface INSIDE the Soekris box. You need to ping 192.168.1.10 to see the result of you pulling the cable. Try to disable the interface in pfsense and your ping will be gone ;)

:D

Derelict

I don't think it's that funny. A Cisco takes the local interface IP address down if it loses carrier, at least by default.

maverick_slo

No this II funny :)

doktornotor

Derelict

Difference of opinion on how a router should actually behave I guess. Neither behavior is wrong. But I would bet the pfSense guys would welcome more Cisco-like behavior if FreeBSD were to implement it. Optional, of course.

Anyway, OP, the reason these guys are bagging on you is easily answered by looking at your diagram. See the ping source, then the ping response, then the connection break FURTHER down the path?

There is really no reason for the router not to respond. The connection break is the next hop.

(Cisco routers do respond in this situation BTW, with an ICMP Destination Unreachable)


R2-2620#ping 192.168.1.1

Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 192.168.1.1, timeout is 2 seconds:
U.U.U

Harvy66

Interface IPs going down can mess with services on the firewall box making is more likely for a service to not rebind to the IP when the interface comes back up. Many services get around this by restarting when a new interface comes up. Many sandbox setups will drop privileges to bind interfaces once the software initializes, meaning the software can't bind to a new IP.

There's many fewer corner cases if you just let the IP stay on the interface even when it's not plugged in. Use a heart beat if you need to check uplink status.

mer

Maybe if one does ifconfig down on the interface after you pull the cable, you get the desired response.

Derelict

Interface IPs going down can mess with services on the firewall box making is more likely for a service to not rebind to the IP when the interface comes back up.

I can certainly see that being a problem.

johnpoz

since when would these IPs go down even in a cisco switch.. Normally your ip would be on loopback or svi, not actually tied to any physical interface.. Can not remember putting an IP on the actual interface before in cisco.. If you were running services on a cisco switch like dhcp or routing even that would be over a SVI, not actually tied to a physical interface being up or down..

phil.davis

I have had switch/router devices before that would stop responding to ping on an interface if the interface was physically down - from memory it was Cabletron/Enterasys gear. Once you knew the behaviour, it meant you knew when the cable had fallen out at a remote place.