Posts Tagged ‘certification’
CCNP Certification / BSCI Exam Tutorial: EIGRP Stuck-In-Active Routes
Passing the BSCI exam and earning your CCNP is all about knowing the details, and when it comes to EIGRP SIA routes, there are plenty of details to know. A quick check in a search engine for “troubleshoot SIA” will bring up quite a few matches. Troubleshooting SIA routes is very challengin in that there’s no one reason they occur.
View the EIGRP topology table with the show ip eigrp topology command, and you’ll see a code next to every successor and feasible successor. A popular misconception is that we want these routes to have an “A” next to them – so they’re active. That’s what we want, right? Active routes sound good, right?
Well, they sound good, but they’re not. If a route shows as Active in the EIGRP topology table, that means that DUAL is currently calculating that route, and it’s currently unusable. When a route is Passive (”P), that means it’s not being recalculated and it’s a usable route.
Generally, a route shown as Active is going to be there for a very short period of time by the time you repeat the command, hopefully that Active route has gone Passive. Sometimes that doesn’t happen, though, and the route becomes SIA – Stuck In Active.
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CCNP Certification / BCMSN Exam Tutorial: Server Load Balancing (SLB)
When you’re working on your BCMSN exam on your way to CCNP certification, you’ll read at length about how Cisco routers and multilayer switches can work to provide router redundancy – but there’s another helpful service, Server Load Balancing, that does the same for servers. While HSRP, VRRP, and CLBP all represent multiple physical routers to hosts as a single virtual router, SLB represents multiple physical servers to hosts as a single virtual server.
In the following example, three physical servers have been placed into the SRB group ServFarm. They’re represented to the hosts as the virtual server 210.1.1.14.
The hosts will seek to communicate with the server at 210.1.1.14, not knowing that they’re actually communicating with the routers in ServFarm. This allows quick cutover if one of the physical servers goes down, and also serves to hide the actual IP addresses of the servers in ServFarm.
The basic operations of SLB involves creating the server farm, followed by creating the virtual server. We’ll first add 210.1.1.11 to the server farm:
MLS(config)# ip slb serverfarm ServFarm
MLS(config-slb-sfarm)# real 210.1.1.11
MLS(config-slb-real)# inservice
The first command creates the server farm, with the real command specifying the IP address of the real server. The inservice command is required by SLB to consider the server as ready to handle the server farm’s workload. The real and inservice commands should be repeated for each server in the server farm.
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CCNP Certification / BCMSN Exam Tutorial: QoS Service Types
To pass the CCNP exams, you’ve got to master Quality of Service, and the first step in doing so is knowing the differences between the different QoS types.
Now this being Cisco, we can’t just have one kind of QoS! We’ve got best-effort delivery, Integrated Services, and Differentiated Services. Let’s take a quick look at all three.
Best-effort is just what it sounds like – routers and switches making their “best effort” to deliver data. This is considered QoS, but it’s kind of a “default QoS”. Best effort is strictly “first in, first out” (FIFO).
An entire path from Point A to Point B will be defined in advance when Integrated Services are in effect. Integrated Services is much like the High-Occupancy Vehicle lanes found in many larger cities. If your car has three or more people in it, you’re considered a “priority vehicle” and you can drive in a special lane with much less congestion than regular lanes. Integrated Services will create this lane in advance for “priority traffic”, and when that traffic comes along, the path already exists. Integrated Services uses the Resource Reservation Protocol (RSVP) to create these paths. RSVP guarantees a quality rate of service, since this “priority path” is created in advance.
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CCNP Certification / BCMSN Exam Tutorial: Getting Started With HSRP
Defined in RFC 2281, HSRP is a Cisco-proprietary protocol in which routers are put into an HSRP router group. Along with dynamic routing protocols and STP, HSRP is considered a high-availability network service, since all three have an almost immediate cutover to a secondary path when the primary path is unavailable.
One of the routers will be selected as the primary (”Active”, in HSRP terminology), and that primary will handle the routing while the other routers are in standby, ready to handle the load if the primary router becomes unavailable. In this fashion, HSRP ensures a high network uptime, since it routes IP traffic without relying on a single router.
The hosts using HSRP as a gateway don’t know the actual IP or MAC addresses of the routers in the group. They’re communicating with a pseudorouter, a “virtual router” created by the HSRP configuration. This virtual router will have a virtual MAC and IP adddress as well.
The standby routers aren’t just going to be sitting there, though! By configuring multiple HSRP groups on a single interface, HSRP load balancing can be achieved.
Before we get to the more advanced HSRP configuration, we better get a basic one started! We’ll be using a two-router topology here, and keep in mind that one or both of these routers could be multilayer switches as well. For ease of reading, I’m going to refer to them only as routers.
R2 and R3 will both be configured to be in standby group 5. The virtual router will have an IP address of 172.12.23.10 /24. All hosts in VLAN 100 should use this address as their default gateway.
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