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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CCIE: PPP Authentication

CCIE: PPP Authentication

Personally, this is an area that I struggled with during my studies. Not quite sure why, the concept is not that difficult. Perhaps, it’s one of those “boring” subjects and I just could not get excited about it no matter how hard I tried. In real world use cases, I used PPP all the time for the PE to CE encapsulation method. The thing is at the SP, there was no need to “secure” the /30 MPLS circuits so, LCP was…

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CCIE: 802.1s (MST)

CCIE: 802.1s (MST)

Overview: MSTP, which uses RSTP for rapid convergence, enables VLANs to be grouped into a spanning-tree instance, with each instance having a spanning-tree topology independent of other spanning-tree instances. This architecture provides multiple forwarding paths for data traffic, enables load balancing, and reduces the number of spanning-tree instances required to support a large number of VLANs. All the details can be found here. My personal field experience: It’s funny, I always hear how great MST is (and it does have…

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CCIE: UDLD

CCIE: UDLD

UDLD is a Layer 2 protocol that enables devices connected through fiber-optic or twisted-pair Ethernet cables to monitor the physical configuration of the cables and detect when a unidirectional link exists. All connected devices must support UDLD for the protocol to successfully identify and disable unidirectional links. When UDLD detects a unidirectional link, it disables the affected port and alerts you. Unidirectional links can cause a variety of problems, including spanning-tree topology loops. UDLD uses it’s own keepalives and not…

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CCIE: Root Guard, BPDU Guard, BPDU Filter, and Loop Guard

CCIE: Root Guard, BPDU Guard, BPDU Filter, and Loop Guard

The BPDU guard feature can be globally enabled on the switch or can be enabled per port, but the feature operates with some differences. At the global level, you enable BPDU guard on Port Fast-enabled ports by using the spanning-tree portfast bpduguard default global configuration command. Spanning tree shuts down ports that are in a Port Fast-operational state if any BPDU is received on them. In a valid configuration, Port Fast-enabled ports do not receive BPDUs. Receiving a BPDU on a Port…

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Internet Blackout

Internet Blackout

I forgot about the blackout until I was looking something up today. Amazing considering how much I use Wiki. Let’s face it, Wiki has become today’s de-facto encyclopedia. Without it, I’d be lost. Tell Congress: Don’t censor the Web! Google Action Page: http://www.foxnews.com/scitech/2012/01/18/wikipedia-goes-dark-for-24-hours-to-protest-us-web-piracy-bills/