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Colby
Colby Glass has been in IT since 2002. He is currently a network engineer with a large Cisco partner and holds the CCNP, CCDP, CCIP, CCNA: Voice, CCNA, JNCIA-ER and ITILv3: Foundations certifications. He has also passed the CCIE R&S Written exam and is studying for the Lab exam.
Posts by Colby
show ip ospf rib
Mar 3rd
Another quick one. Today I’m going to cover a simple, but very useful OSPF command: “show ip ospf rib”. This command is similar to “show ip route ospf”, but goes a bit deeper.
If you’ve ever done a routing protocol migration, you know how important it can be to see each protocol’s full routing table. Much of the time AD makes this difficult. Administrative Distance (AD) is the believability of a routing protocol on a Cisco device. The default AD values are:
Route Source |
Default Distance |
| Connected Interface | 0 |
| Static Route | 1 |
| EIGRP Summary | 5 |
| eBGP | 20 |
| Internal EIGRP | 90 |
| IGRP | 100 |
| OSPF | 110 |
| IS-IS | 115 |
| RIP | 120 |
| EGP | 140 |
| ODR | 160 |
| External EIGRP | 170 |
| iBGP | 200 |
| Unknown | 255 |
Firewall Object Groups
Mar 2nd
Dropping in to do a quick post today. Sorry for the ridiculous lack of content lately. I’ve been busy with finding/changing jobs and new responsibilites and all that.
Today I’m going to cover “object groups” on ASAs. I was never a big fan of these, which I realized had a lot to do with using them behind others, not actually writing them myself. It takes awhile (for me, at least) to wrap your head around what the person before you was trying to accomplish. This is what put me off object groups. Though, I discovered that if I write them myself, I love them, lol. They can be hugely useful. They’re even available in IOS now (as of 12.4(20)T). Here’s an example of when they’d be used:
CCNA Scholarship
Sep 16th
Steve is doing another generous offering over at Networking Forum. He’s planning to give away a “scholarship” for the CCNA. He will essentially pay someone’s way through the CCNA if this person agrees to log his or her progress on the forum. We, the staff and member base, are also offering our guidance and support throughout the process. Here’s a snippet from the forum:
What’s going on?
networking-forum.com is offering a scholarship to one person who would like to earn a Cisco Certified Network Associate (CCNA) certification. The scholarship will provide the CCNA Official Exam Certification Library, a separate forum specifically dedicated to the candidate for his or her use during their studies with feedback from the site’s members, and reimbursement of the exam fees after they pass their exam(s).
How is the recipient chosen?
Fiber Woes
Sep 7th
I’m in the process of doing a very large hardware refresh for my company. We’re replacing 100+ old/EOL switches throughout the network/country. This shouldn’t be too big of a deal, but the latest generation of Cisco switches use SFPs. The older stuff is all GBIC. For most of our large sites, this isn’t major as we just run an ST to LC cable from the patch panel to the switch…
But of course, there are random sites without patch panels. The fiber runs directly from switch to switch. This presents a problem as we don’t have detailed information for most of our sites. So the options are re-terminating the ends of the fiber, buying a long enough patch cable (difficult to do) or having someone come out and pull new runs. That was until I came across these:
Tripp Lite N458-001-50 Duplex Multimode 50/125 Fiber Adapter, LC-M/SC-F – 1ft
%C4K_EBM-4-HOSTFLAPPING
Aug 26th
This means loop!
A coworker came to me with an issue today. He asked if I’d ever seen this before and showed me:
.Aug 25 22:44:29 UTC: %C4K_EBM-4-HOSTFLAPPING: Host 00:00:85:DE:15:61 in vlan 54 is flapping between port Gi2/4 and port Gi2/2 .Aug 25 22:44:59 UTC: %C4K_EBM-4-HOSTFLAPPING: Host 00:00:85:DE:15:61 in vlan 54 is flapping between port Gi2/4 and port Gi2/2 .Aug 25 22:47:42 UTC: %C4K_EBM-4-HOSTFLAPPING: Host 00:00:85:DE:15:61 in vlan 54 is flapping between port Gi2/4 and port Gi2/2 |
I said “it means there’s a loop, give me the switch IP”. Then I began the mission of tracking down the loop. This was a pretty large site, but luckily I only had to go through a couple switches. Unfortunately this happened a couple hours ago and I didn’t save my work so we won’t be able to go through the real steps.
To track down a loop, you start with the “show mac-address-table address [flapping mac]” command:
SW1#sh mac-add add 0000.85de.1561
Unicast Entries
vlan mac address type protocols port
-------+---------------+--------+---------------------+--------------------
1 0000.85de.1561 dynamic ip GigabitEthernet2/2
54 0000.85de.1561 dynamic ip GigabitEthernet2/4 |
We see that the MAC is coming in on port gi2/2 and gi2/4. One port will lead us to where that MAC is plugged in and the other will lead us to the loop. Pick a port and start working through. This is where CDP comes in handy:
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