Hi. Two of my company's routers, are connected with 2 serial connection with each other. No multi link interfaces are defined. Serial 0 works fine, but Serial 1, after issuing "no shut" command, works couple of seconds, and change it's state to "Serial1 is up, line protocol is down". Both routers running EIGRP. Is this problem is L1 issue, or maybe EIGRP protocol have something with blocking interfaces to prevent some kind of loop? Second part of problem is that branch office router, configured with EIGRP and same AS number as rest of routers, does not have any routes learned dynamically... To one who is interested to help, I can send short config output for EIGRP, ACL, etc.