MST w/ PVST+
larue38462
Member Posts: 32 ■■□□□□□□□□
in CCNP
So I'm at the labbing phase of my studies for 642-813. I've read through the FLG once and read the cert guide and took notes on it. I'm in the process of working through the Lab Manual and re-reading the FLG while doing so. Tonight I was labbing up some STP, RSTP, and MST and all went well until I got into MST.
I went by the lab manual with no problems for all 3 flavors of STP and even reviewed my notes and the cert guide while doing my lab. After I finished my MST only lab, I decided to play a little more and try to incorporate MST on two switches (3560s) with two other switches (3550s) running PVST+.
This is how my network was configured when I began incorporating MST with PVST+:
For the two PVST+ switches, I had one configured as the root for vlan 5 and the other configured for the root for vlan 10. The trunks from the PVST+ switches to the MST regions (or the IST) allowed all vlans.
For the MST switches, I just used the two instances configured from my MST only lab. MST region 1 mapped to vlans 10,20,30 and MST region 2 mapped to vlans 40,50,60. One switch was the root for region 1 and the other was root for region 2.
Connectivity to/between the mst switches was fine, but connectivity to both PVST+ switches was lost. Looking at the output of the show spanning-tree vlan 1 and show spanning-tree vlan 5 on the MST switches showed the RP for each vlan was in BKN* status and showed *PVST_Inc. I verified that the trunks matched up perfectly and could find nothing further in either the FLG or the Cert Guide on why this was happening.
After some further research through Cisco docs, I found that the root bridge for the VLANs on PVST+ switches must be inside the MST region (region 0).
In an attempt to fix the issue, I tried to issue the spanning-tree vlan 1 root primary and spanning-tree vlan 5 root primary cmds on the mst switches. After looking at the show spanning-tree vlan 1 and 5 output, I was confused to see that the command did nothing to change the bridge priority for either vlan and the switch didn't become root for either (and of course both of the PVST+ switches showed they were still the root for their respective VLANs).
At this point I went to the PVST+ switches with a console cable and manually set the priority for the respective vlans to 61440. Again, this did nothing in regard to the bridge priority to the PVST+ switches. Finally, I got lucky when I issued the spanning-tree MST 0 root primary command, which made the local MST switch the root for ALL vlans not mapped to an MST instance (other than MST 0/the IST).
Sorry that this post was so long, but it took me forever to figure this out and I went back through the FLG and the cert guide and didn't see anything about the MST region switches needing to be the root for all of the PVST+ switch vlans. I'm going to look again tomorrow because I like to have faith in the text issued by the testing company, but at this point I really won't be shocked if I fail to find it again. If anyone else has read through the guides and picked up on something that I didn't, please pass along the page numbers where you found it or if anyone sees something I was doing wrong here, please feel free to set me straight. After all this, I think I'll end the lab on somewhat of a high note since at least I found out where I was screwing up. Thanks in advance for any replies.
I went by the lab manual with no problems for all 3 flavors of STP and even reviewed my notes and the cert guide while doing my lab. After I finished my MST only lab, I decided to play a little more and try to incorporate MST on two switches (3560s) with two other switches (3550s) running PVST+.
This is how my network was configured when I began incorporating MST with PVST+:
For the two PVST+ switches, I had one configured as the root for vlan 5 and the other configured for the root for vlan 10. The trunks from the PVST+ switches to the MST regions (or the IST) allowed all vlans.
For the MST switches, I just used the two instances configured from my MST only lab. MST region 1 mapped to vlans 10,20,30 and MST region 2 mapped to vlans 40,50,60. One switch was the root for region 1 and the other was root for region 2.
Connectivity to/between the mst switches was fine, but connectivity to both PVST+ switches was lost. Looking at the output of the show spanning-tree vlan 1 and show spanning-tree vlan 5 on the MST switches showed the RP for each vlan was in BKN* status and showed *PVST_Inc. I verified that the trunks matched up perfectly and could find nothing further in either the FLG or the Cert Guide on why this was happening.
After some further research through Cisco docs, I found that the root bridge for the VLANs on PVST+ switches must be inside the MST region (region 0).
In an attempt to fix the issue, I tried to issue the spanning-tree vlan 1 root primary and spanning-tree vlan 5 root primary cmds on the mst switches. After looking at the show spanning-tree vlan 1 and 5 output, I was confused to see that the command did nothing to change the bridge priority for either vlan and the switch didn't become root for either (and of course both of the PVST+ switches showed they were still the root for their respective VLANs).
At this point I went to the PVST+ switches with a console cable and manually set the priority for the respective vlans to 61440. Again, this did nothing in regard to the bridge priority to the PVST+ switches. Finally, I got lucky when I issued the spanning-tree MST 0 root primary command, which made the local MST switch the root for ALL vlans not mapped to an MST instance (other than MST 0/the IST).
Sorry that this post was so long, but it took me forever to figure this out and I went back through the FLG and the cert guide and didn't see anything about the MST region switches needing to be the root for all of the PVST+ switch vlans. I'm going to look again tomorrow because I like to have faith in the text issued by the testing company, but at this point I really won't be shocked if I fail to find it again. If anyone else has read through the guides and picked up on something that I didn't, please pass along the page numbers where you found it or if anyone sees something I was doing wrong here, please feel free to set me straight. After all this, I think I'll end the lab on somewhat of a high note since at least I found out where I was screwing up. Thanks in advance for any replies.
Currently studying for Route. Shooting for a 6/3/11 test date.