A while back I was responsible for setting up a group of switches and routers to serve as the internet distribution for a hospital, mainly the function of designing the IGP of choice to work given the hospital’s requirements and coordinating with the teardown of the old gear. The idea was to configure EIGRP so that one next-hop was preferred over another. We know this is possible through tweaking the various metrics for a given IGP, but in the process, I was reminded of something that’s quite important to think about when doing so.
A while back I was responsible for setting up a group of switches and routers to serve as the internet distribution for a hospital, mainly the function of designing the IGP of choice to work given the hospital’s requirements and coordinating with the teardown of the old gear. The idea was to configure EIGRP so that one next-hop was preferred over another. We know this is possible through tweaking the various metrics for a given IGP, but in the process, I was reminded of something that’s quite important to think about when doing so.
A while back I was responsible for setting up a group of switches and routers to serve as the internet distribution for a hospital, mainly the function of designing the IGP of choice to work given the hospital’s requirements and coordinating with the teardown of the old gear. The idea was to configure EIGRP so that one next-hop was preferred over another. We know this is possible through tweaking the various metrics for a given IGP, but in the process, I was reminded of something that’s quite important to think about when doing so.
I wrote an article a while back regarding VLAN configuration when running vSphere ESXi on top of Cisco UCS.
A comment pointed out that all vNICs are automatically configured as trunks. I had not heard of this before, so I got into the CLI to take a look.
Here’s a VLAN configuration screen in the UCSM GUI for a sample vNIC:
Check out the running configuration for this vNIC on the underlying NX-OS CLI.
I wrote an article a while back regarding VLAN configuration when running vSphere ESXi on top of Cisco UCS.
A comment pointed out that all vNICs are automatically configured as trunks. I had not heard of this before, so I got into the CLI to take a look.
Here’s a VLAN configuration screen in the UCSM GUI for a sample vNIC:
Check out the running configuration for this vNIC on the underlying NX-OS CLI.
A little detour from the networking topics today to show off a little weekend tech project.
I recently ran into some overheating problems with my home BYO PC. Core Temp was showing upwards of 70 degrees Celsius during normal operation, and under load, it would sometimes just shut down completely.
Here’s the setup I had as of 2 days ago:
The rear fan, which takes air in, was not working due to a short.
A little detour from the networking topics today to show off a little weekend tech project.
I recently ran into some overheating problems with my home BYO PC. Core Temp was showing upwards of 70 degrees Celsius during normal operation, and under load, it would sometimes just shut down completely.
Here’s the setup I had as of 2 days ago:
The rear fan, which takes air in, was not working due to a short.
I have always used the “network 0.0.0.0 0.0.0.0” statement to describe “all interfaces” when configuring a routing protocol like EIGRP. I know that it’s not correct, but I never stopped to wonder why my bad habit still worked.
Then, I found this good article by @jdsilva explains this is IOS just assuming you had a “brain fart” and meant to type the proper “network 0.0.0.0 255.255.255.255”
I’m studying for the CCIE and it can be really good to identify these bad habits that, while in real life may not be too bad, especially this kind, where the result is the same, but on exams can mean the difference between failure and success.
I have always used the “network 0.0.0.0 0.0.0.0” statement to describe “all interfaces” when configuring a routing protocol like EIGRP. I know that it’s not correct, but I never stopped to wonder why my bad habit still worked.
Then, I found this good article by @jdsilva explains this is IOS just assuming you had a “brain fart” and meant to type the proper “network 0.0.0.0 255.255.255.255”
I’m studying for the CCIE and it can be really good to identify these bad habits that, while in real life may not be too bad, especially this kind, where the result is the same, but on exams can mean the difference between failure and success.
This is a specific video on Rapid Spanning Tree Synchronization.
See my full writeup on RSTP in general.
Forgive the low(er) quality of this particular video, it was recorded at an hour in the morning that frankly should not exist.
This post picks up where the previous left off. Again, a CCNP-level knowledge of STP is recommended.
So…Spanning Tree didn’t converge quickly enough for some people, and enabling PortFast everywhere kind of defeats the purpose, so 802.1w Rapid Spanning Tree was born. RSTP in essence puts into place some additional features to speed up STP reconvergence. Old-school 802.1D meant that you had to wait at least 30 seconds to get a port from blocking to forwarding, and this means that recovering from a failure takes at least that much time (sometimes more depending on other factors).
This is a specific video on Rapid Spanning Tree Synchronization.
See my full writeup on RSTP in general.
Forgive the low(er) quality of this particular video, it was recorded at an hour in the morning that frankly should not exist.
This post picks up where the previous left off. Again, a CCNP-level knowledge of STP is recommended.
So…Spanning Tree didn’t converge quickly enough for some people, and enabling PortFast everywhere kind of defeats the purpose, so 802.1w Rapid Spanning Tree was born. RSTP in essence puts into place some additional features to speed up STP reconvergence. Old-school 802.1D meant that you had to wait at least 30 seconds to get a port from blocking to forwarding, and this means that recovering from a failure takes at least that much time (sometimes more depending on other factors).
This is a specific video on Rapid Spanning Tree Synchronization.
See my full writeup on RSTP in general.
Forgive the low(er) quality of this particular video, it was recorded at an hour in the morning that frankly should not exist.
This post picks up where the previous left off. Again, a CCNP-level knowledge of STP is recommended.
So…Spanning Tree didn’t converge quickly enough for some people, and enabling PortFast everywhere kind of defeats the purpose, so 802.1w Rapid Spanning Tree was born. RSTP in essence puts into place some additional features to speed up STP reconvergence. Old-school 802.1D meant that you had to wait at least 30 seconds to get a port from blocking to forwarding, and this means that recovering from a failure takes at least that much time (sometimes more depending on other factors).
This is a video on some of the “nerd knobs” that we get to play with in a traditional spanning tree environment.
I have done a full writeup on the topic that goes along with this video - you can view this video on that page as well.
I wrote this post not only to put out some information on one of the least-understood facets of networking (especially in data center, as most technology today is aimed at making STP irrelevant) but also to help get something on paper for me, seeing as I am going down the CCIE path full force now, and this has always been a weak area of mine. This post will assume you have CCNP-level knowledge about Spanning Tree Protocol (STP).
This is a video on some of the “nerd knobs” that we get to play with in a traditional spanning tree environment.
I have done a full writeup on the topic that goes along with this video - you can view this video on that page as well.
I wrote this post not only to put out some information on one of the least-understood facets of networking (especially in data center, as most technology today is aimed at making STP irrelevant) but also to help get something on paper for me, seeing as I am going down the CCIE path full force now, and this has always been a weak area of mine. This post will assume you have CCNP-level knowledge about Spanning Tree Protocol (STP).
This is a video on some of the “nerd knobs” that we get to play with in a traditional spanning tree environment.
I have done a full writeup on the topic that goes along with this video - you can view this video on that page as well.