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Month: February 2012

CCIE: BGP

CCIE: BGP

Unlink IGP’s, BGP does not use metrics to select best path. Instead, BGP is vector based. This path is determined with Path Attributes (PA’s). The default PA, if no others are set is AS-PATH. Shortest path to destination prefix is the best path. Building the neighbor relationship: TCP Port 179 (established based on neighbor address), Open, Established, and finally Updates (contains the prefix information). If there is a problem/error a “notification” message is sent. Keepalive is 60 and hold time is…

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CCIE: RIP

CCIE: RIP

Notes: auto-summary in RIP affects what is advertised, but not the local RIB. Preventing route feedback: Prevent router feedback (RIP) with static route to null0 or distribute-list (IN) on originating router. interface> ip rip advertise (interval different than the global) default sent out specific interface: use route-map that sets interface and default-information originate. DON’T FORGET ABOUT ROUTE FEEDBACK IN RIP! ACL to filter even/odd octets: ip access permit 0.0.1.0 255.255.254.255 : permit 3rd octet odd only ip access permit 0.0.0.0 255.255.254.255…

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CCIE: GRE Tunneling/Recursive Routing

CCIE: GRE Tunneling/Recursive Routing

Here is a subject and burned me in my last lab. I had a much more complex environment, but the fundamentals are the same. Recursive routing errors occur when the tunnel destination is dynamically learned across the tunnel interface itself. Here are two simple methods to correct this behaivor. 1) Static route to the tunnel destination via any interface/path, but the tunnel interface (lower metric then a dynamic learned IGP). On the CCIE lab static routes are generally a no-no, that being…

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CCIE: OSPF

CCIE: OSPF

The Basics: Link state routing protocol. Uses IP protocol 89. Hellos sent on 224.0.0.5. Uses Dijkstra SPF algorithm independently on each router against the local LSDB to calculate the best routes. Hellos sent every 10 seconds on LAN and 30 seconds on WAN interfaces. Dead time is 4x hello, so 40sec and 120 sec respectively. Router ID: 1) Configured “router id” 2) Highest loopback 3) Highest non loopback interface in up/up state. Hello Process Sanity check: Pass authentication (verify with “debug ip ospf adj”)…

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CCIE: EIGRP

CCIE: EIGRP

One of my favorite routing subjects to discuss. Usually, I’ll be asked what is a better IGP OSPF or EIGRP and my answer is always… it depends. There a couple compelling reasons why EIGRP is still a great IGP after so many years. Here are a few in my opinion; ease of deployment, convergence speed (without tweaks), and offset capability. Of course, there are some disadvantages; scale, ease of deployment (your not required to take a deep look at your topology like OSPF), and it’s proprietary….

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