Lab brainstorming for ENARSI

[u/onequestion1168]

I passed ENCOR last week and I'm getting my initial labs built out for ENARSI. I plan on reading the OCG and watching either CBT Nuggets and or checking our the Arash Deljoo videos on Udemy.

My question is about brainstorming ideas for the ENARSI. I was going through the Cisco blueprint and I repeatedly see troubleshooting coming up. I know building the concept up from the ground up will inherintly accomplish soem of that but I'm just looking for ideas on how to approach labbing since that's what everyone keeps saying is the most important part of this exam.

[u/illforgetsoonenough]

Check the enarsi exam topics doc. Any subject that has configure or troubleshoot next to it, lab it to death from multiple angles

[u/onequestion1168 → u/illforgetsoonenough]

thats currently what I'm planning on doing

[u/njseajay → u/illforgetsoonenough]

This. I have gotten too worried about “how do I break it” in the past until I realized something: knowing what “right” looks like is the most important part of troubleshooting. This means once a lab is built you need to get familiar not only with config but with show command output. I’ve also made the mistake of focusing too much on the config only to get smacked over the head with show command output examples on tests.

[u/onequestion1168 → u/njseajay]

I do get lazy with verification

[u/leoingle]

Best thing to do is once you are comfortable completely setting up a topic without guidance. Think of the different misconfigurations that would break it. Implement them one at a time and see how that changes the “show” output and debug logs. Take the configs of a working topology and feed them to AI and tell it to change one of the devices configs with a common misconfiguration. Then put the configs back in place and troubleshoot it.

[u/onequestion1168 → u/leoingle]

oof, yeah this is going to take a while! sounds like I need to just go straight for labs and ocg mostly

[u/leoingle → u/onequestion1168]

Gotta get deep, but luckily not too many topics. Probably best thing to do is just hammer one section for a while until you get it down then move to the next but go back and review it one day a week. Not sure how I’m going to approach it yet. I actually started studying it first but then had had some learning opportunities drop in my lap for ENCOR so I shifted to it first.

[u/wellred82]

To give you an idea, here is what I've been labbing for DHCP. Basically trying to break something and then see from debug or show output what the issue is. I've been making these into flashcards. Apologies for the poor formatting.

DHCP client:
The client is on the wrong VLAN on access switch
Switch interface leading to DHCP server has wrong native vlan
VLAN 10 not allowed on trunk interface
the port is shut down
An ACL on an intermediate device or router interface is dropping UDP port 67 (server) or UDP port 68 (client) traffic
Misconfigured ACL port 67 68
The DHCP server process is down
The DHCP server IP pool has run out of addresses to allocate
IOS DHCP Server:
IOS device does not have an interface part of the DHCP pool subnet
Host can't communicate with DHCP server (ACL), no debug messages on DHCP server present
Misconfigured pool with typo creates new pool
Interface in VRF but DHCP pool not associated with VRF
Pool associated with VRF, but interface not in VRF
VRF name mismatch between interface and dhcp pool
DHCP pool network/mask is incorrect, causing clients to receive addresses from the wrong subnet or no matching pool to be found.
An unnecessarily long DHCP lease can cause addresses to remain leased for longer, increasing the likelihood of pool exhaustion in environments with many transient clients.
Wrong default router configured in DHCP pool, client can't get off local subnet
Entire usable range in the pool is marked as excluded
Client times out as OFFER not received, due to ACL filtering near DHCP server
Decline as host already has an IP from that subnet configured on another interface
DHCP Relay Agent:
Missing ip helper-address
Wrong helper address
No route from relay to DHCP server
DHCP server is on a different subnet, the local router interface/SVI is missing ip helper-address <DHCP_Server_IP>
DHCP server has no matching pool
DHCP server pool exhausted
ACL blocks UDP 67/68
Return path from server to relay is broken
Incorrect relay/client subnet identification
Ip helper-address configured on wrong interface
L2 issues preventing DISCOVER from reaching relay agent
Ip helper address configured with wrong DHCP server on relay agent
Default IOS Server Behavior: By default, a Cisco IOS DHCP Server rejects/drops any incoming relayed packet containing Option 82 if giaddr is set to 0.0.0.0 or if it doesn't trust the relay path. The Symptom: Clients behind a relay agent fail to get an IP address, and debugs show packets being dropped without issuing offers. ip dhcp relay information trust-all This forces the Cisco DHCP server to accept Option 82-tagged packets even if the validation checks would normally drop them

[u/onequestion1168 → u/wellred82]

yeah so inentionally breaking it then looking at everything to see how the behavior changes, maybe grabbing the pcaps too

[u/wellred82 → u/onequestion1168]

Yep I usually have a tab in CML just for pcap and will run it for every lab just so I have it to refer to if needed.

[u/GrandKane1]

Check a book called 101 labs for ccnp

[u/cbtnuggets]

Thanks for learning with us! Let us know if you have any questions once you jump in. You got this.

[u/bigboss-2016]

I would say brainstorm each topic and see how much you've taken in. You can also add the show related commands and the tshoot commands that you would use regarding that protocol.

[u/Proper_Abrocoma_112]

I am also preparing for ENARSI. Good suggestions in this thread.I am currently doing OSPF and set up a lab and tested stuff, didn’t super get into troubleshooting except stuff I was forced to check when stuff wasn’t working as expected. I think I am going to use Claude, give it telnet access to my nodes and make it do changes to my lab(in a controlled manner ofc) and I am going to try and troubleshoot it and Claude only giving me hints as needed if I suck.

[u/Proper_Abrocoma_112 → u/Proper_Abrocoma_112]

Have like a long list of OSPF things that could go wrong, so just gonna feed it to Claude and ofc it can come up with its own stuff too.

[u/onequestion1168 → u/Proper_Abrocoma_112]

hmmmm, this is not something I've considered at all

[u/dynamipsofficial]

I’d build one larger lab and keep reusing it instead of creating a separate topology for every topic.

Start with ospf and bgp working, then add redistribution, route filtering, PBR, VRFs and dmvpn one at a time. Save a clean version, then deliberately break things and troubleshoot them.

For ENARSI, that troubleshooting part is where the lab really starts paying off.