Network issue while connecting linux server

When we connect linux server in intermet that time my all office network goes down we have changed ip address also I m not able to find out the issue pls help me asap

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1-connect only local nic port and chk,if it working properly then
2-connect 2nd nic port and chek again.
Do this for identify which nic port is having issue.

Also check if this server is having live ip then block all open port in iptables.

One more thing.
Check broadcasting and subnet of given ip