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Category: CCIE Studies

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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CCIE: STP (802.1d)

CCIE: STP (802.1d)

So, first a little history on Spanning tree protocol (STP). Based on an algorithm created by Radia Pearlman in 1985. http://en.wikipedia.org/wiki/Radia_Perlman Became a standard IEEE protocol in 1990. Still widely deployed. Flavors of spanning tree. 802.1d (ieee), 802.1w (rapid), and 802.1s (mst). Evolution of STP, Cisco vPC (2-way non blocking, still requires STP) and Fabric Path (eliminates STP completely). TRILL is a standardized version of Fabric Path. Both TRILL and Fabric Path utilize a link state protocol (IS-IS) as their loop prevention method. Specific Cisco enhancement to 802.1d (prior to 802.1w):…

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CCIE: 802.1q (QinQ tunneling/802.1ad)

CCIE: 802.1q (QinQ tunneling/802.1ad)

One of my personal favorite L2 subjects to discuss. When I was at the service provider this was a very cost effective Metro solution to extend customer VLANs. No routing protocols on the CPE and no expensive EoMPLS hardware required from the SP perspective. Simple and effective. You will hear many names for the outer tag (S-TAG, metro tag, etc…) just remember that the outer tag is the unique SP ID for that customer and the inner tags are the…

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CCIE: VTP or not to VTP, that is the question.

CCIE: VTP or not to VTP, that is the question.

In *most* productions networks device limitations (VLAN,TCAM entries) must be taken into consideration. This is one of the downsides of using VTP. All switches will get the entire database regardless if they have local assignments or even are in the transit L2 path. Transparent mode and manually creating the necessary VLANs may be your best option. Switches to not create a STP instance for unnecessary VLANs thus conserving resources and CPU cycles. If you are using VTP be sure to enable pruning to conserve bandwidth…

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