Score:0

Network Connectivity Problem after changing IP

cn flag

I have a weird problem

I have two networks (Site A) and (Site B) connected via a cisco router

Site A has pcs like A1, A2, A3 Site B has pcs like B1, B2 (Windows Server) , B3 (Ubuntu 18.04.5)

All pcs can ping to each other and all is fine.

If I change the ip of B2 to be anything else in the subnet all pcs can ping to each other and all is fine.

If however I change the ip of B3 to be anything else, all pcs of Site B can ping to B3 but none of the pcs of Site A can ping B3. Then after some amount of time (I am not sure but 15 to 20 minutes) all pcs of Site A start to ping B3 without any further change.

I suspect it has something to do with the arp cache of the router but the people who manage the router simply argue, it works as expected in windows so its your linux problem.

I have tried with two ubuntu linux machines and both show the same problem. Now I am lost, any lead would be highly appreciated. Thanks.

raj avatar
cn flag
raj
It looks like your Ubuntu does not send the **gratuitious ARP** packet that informs other devices in the network (including routers) that the IP address has changed. How do you change the IP address? Do you simply change it with `ifconfig` or do you change it in Network Manager settings, bring down the interface and bring it up again? When you bring down the interface and bring it up again, the gratuitious ARP should be sent. You can also send a gratuitious ARP manually using the `arping` tool: https://www.cyberciti.biz/faq/linux-networking-sending-gratuitous-arps/
user9082746 avatar
cn flag
@raj In the past I have even tried to restart the server and still it didn't ping on the changed IP. I will try the link you have posted and update you. On the side note both Ubuntu's were fresh installs but not updated as they don't have internet access.
raj avatar
cn flag
raj
It is possible that it is indeed some router misconfiguration, but your router people are simply lazy or incompetent and don't want to bother with your problem, because from their point of view a "typical" user (read: Windows user) does not have a problem.
mangohost

Post an answer

Most people don’t grasp that asking a lot of questions unlocks learning and improves interpersonal bonding. In Alison’s studies, for example, though people could accurately recall how many questions had been asked in their conversations, they didn’t intuit the link between questions and liking. Across four studies, in which participants were engaged in conversations themselves or read transcripts of others’ conversations, people tended not to realize that question asking would influence—or had influenced—the level of amity between the conversationalists.