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CCNP / BCMSN Tutorial: BPDU Skew Detection Okay, I know what you're thinking! "What the heck is a BPDU Skew, and why do I want to detect it?" There is no "BPDU Skew" -- what we're trying to detect are BPDUs that are not being relayed throughout the network as quickly as they should be. The root bridge is the only switch that's sending original BPDUs; the non-root switches relay that BPDU down the STP tree. This should happen quickly thorughout the network, since the root bridge will be sending a BPDU every two seconds by default ("hello time"), and the switches should relay the BDPUs fast enough so every switch is seeing a BPDU every two seconds. That's in a perfect world, though, and there are plenty of imperfect networks out there! You may have a busy switch that can't spare the CPU to relay the BDPU quickly, or a BPDU may just simply be lost in transmission. That two-second hello time value doesn't give the switches much leeway, ...

Monday's CCNA / CCNP Practice Questions: CCNA: What devices typically make up a Frame Relay cloud? A. Frame Relay routers (DCEs) B. Frame Relay routers (DTEs) C. Frame Relay switches (DCEs) D. Frame Relay switches (DTEs) BSCI: What is the highest AS number available in the BGP private AS range? A. 64512 B. 64555 C. 65535 D. 65555 E. 32768 BCMSN: Which of the following interface-level commands enables Loop Guard? A. spanning-tree loop guard B. spanning-tree guard loop C. loop guard run D. loop guard enable E. run loop guard F. enable loop guard Chris Bryant CCIE #12933 www.thebryantadvantage.com

Answers To Saturday's CCNA / CCNP Practice Questions CCNA: Which two of the following phrases best describe fragment-free switching? A. No error checking B. Some error checking C. Looks only at destination MAC before beginning to forward the frame D. Looks at the first 64 bytes of the frame before beginning to forward the frame ANSWER: B, D. Fragment-free switching looks at the first 64 bytes of the frame before forwarding it. This offers limited error protection, since most frame errors occur within the first 64 bytes. It's not as thorough as store-and-forward , which runs a Cyclical Redundancy Check before forwarding a frame, but it's better than cut-through switching , which offers no error checking. BSCI: By default, how does an OSPF routing table indicate routes that were learned via redistribution? A. O E1 B. O E2 C. O EX D. O ANSWER: B. OSPF routes learned via redistribution are marked as O E2, or External type-2. BCMSN: What is the range of physical connections tha...

CCNP / BCMSN Tutorial: UplinkFast When you're studying for the BCMSN exam, you can get overwhelmed with trying to keep UplinkFast, PortFast, BDPU Guard, Loop Guard, and other guards and loops straight! Today, we'll spend a few minutes with an introduction to UplinkFast. You remember from your CCNA studies that when a port goes through the transition from blocking to forwarding, you're looking at a 50-second delay before that port can actually begin forwarding frames. Configuring a port with PortFast is one way to get around that, but again, you can only use it when a single host device is found off the port. What if the device connected to a port is another switch? A switch can be connected to two other switches, giving that local switch a redundant path to the root bridge, and that's great - we always want a backup plan! However, STP will only allow one path to be available, but if the available path to the root switch goes down, there will be a 50-second delay due to ...

Saturday's CCNA / CCNP Practice Questions CCNA: Which two of the following phrases best describe fragment-free switching? A. No error checking B. Some error checking C. Looks only at destination MAC before beginning to forward the frame D. Looks at the first 64 bytes of the frame before beginning to forward the frame BSCI: By default, how does an OSPF routing table indicate routes that were learned via redistribution? A. O E1 B. O E2 C. O EX D. O BCMSN: What is the range of physical connections that can be bundled into an Etherchannel? A. One to eight B. Two to eight C. Two to ten D. Three to eight E. Three to ten Chris Bryant CCIE #12933 www.thebryantadvantage.com

Friday's CCNA / CCNP Questions And Answers CCNA: What is the network mask for a Class A address? A. 255.255.255.255 B. 255.255.255.0 C. 255.255.0.0 D. 255.0.0.0 E. /8 F. /12 G. /16 H. /24 ANSWER: D, E. 255.0.0.0 and /8 are the classful masks for Class A networks. They're the same mask, expressed in both dotted decimal (255.0.0.0) and prefix notation (/8). BSCI: Which of the following values does NOT have to be agreed upon between potential OSPF neighbors in order for an adjacency to be created? A. The process number. B. The area number. C. The hello and dead timers. D. The stub flag setting. ANSWER: A. The OSPF process number is locally significant only. Routers must agree on the area number, the timers, and the stub flag setting to become neighbors. BCMSN: Which of the following is designed to detect unidirectional links? A. Root Guard B. Loop Guard C. BackboneFast D. UDLD E. UplinkFast F. BPDU Guard ANSWER: D. UDLD, or Unidirectional Link Detection, does just that!

Cisco CCNA Tutorial: The OSPF RID OSPF is a major topic on your CCNA exam, as well it should be. OSPF is a widely-used WAN protocol, and you need to learn the fundamentals before moving on to more complicated configurations. One such detail is the OSPF Router ID, or RID. The RID is the dotted decimal value by which other OSPF routers will identify a given OSPF router. There are some interesting defaults for this value, and a command you should know to hardcode the RID. You had also better know what has to happen for this command to take effect! In this example, R1 has an adjacency with R2 and R3 over the 172.12.123.0/24 frame network. R1 is the hub, with R2 and R3 as the spokes. No other interfaces are OSPF-enabled on any of the routers. Running show ip ospf neighbor on R1, we see some unusual values under "Neighbor ID", which is another name for the OSPF RID. R1#show ip ospf neighbor Neighbor ID Pri State Dead Time Address Interface 3.3.3.3 0 FULL/DROTHER 00:01:57 172.12.123...