UDP packet not getting received on Centos 6.7 using Floating IP

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Apurv
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UDP packet not getting received on Centos 6.7 using Floating IP

Post by Apurv » 2018/08/30 05:38:05

I have plumbed a Floating IP on my CentOS 6.7. IP is pingable from all the machines on LAN. On the same host, there is one UDP Server and a UDP client where both of them are using this FIP(Floating IP). Now, UDP server sends a UDP packet to UDP client but somehow UDP client didn't receive the packet. However, the packet is visible in Tcpdump/Wireshark and all the headers (Ethernet , MAC, IP, and UDP ) seems alright.
Can anyone suggest how to proceed?

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avij
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Re: UDP packet not getting received on Centos 6.7 using Floating IP

Post by avij » 2018/08/30 12:14:31

I would run "yum update", then reboot.

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TrevorH
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Re: UDP packet not getting received on Centos 6.7 using Floating IP

Post by TrevorH » 2018/08/30 13:45:26

Also, tcpdump/wireshark "sees" the packet before any firewall has inspected it and possibly dropped or rejected it.
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jlehtone
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Re: UDP packet not getting received on Centos 6.7 using Floating IP

Post by jlehtone » 2018/08/31 13:06:50

What is a "Floating IP"?

Does that IP resolve to a name? Does that name resolve to the IP?


If the destination of a packet is any of the IP addresses of the localhost, then the packet is routed to the loopback device (lo). The default CentOS 6 firewall ruleset starts:

Code: Select all

-A INPUT -m state --state RELATED,ESTABLISHED -j ACCEPT 
-A INPUT -p icmp -j ACCEPT 
-A INPUT -i lo -j ACCEPT
Yes, the loopback should accept all.

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