Yuri Slobodyanyuk's blog on IT Security and Networking sharing experience and expertise

Category: IOS Cisco (page 1 of 3)

How to enroll VPN client with IOS CA

If you didn’t notice Cisco IOS routers can serve as CA servers as well. The example configurations are easy to find on the cisco.com but the only trick to know when enrolling Cisco VPN client with IOS CA is the syntax you put as url – the string should look:
I attach below screenshot so you can see what I mean.
Some references as well .

URL to use when enrolling with Cisco CA

PKI client enrol with cisco CA

Archive IOS running configuration automatically for possible rollback

Here is a feature that will save you time and frustration in many possible scenarios – especially when managing Cisco routers in multi-user environment. Once enabled archiving saves periodically copy of the running configuration of IOS router to the flash or remote server. So
next time something stops working after changes and you don’t know which one caused this – just revert back to the working configuration that is readily available.

Configure DVTI hairpinning on Cisco router for safe browsing

guten Tag everyone, today i am posting the video showing how to configure Dynamic Virtual Tunnel Interface (DVTI) on Cisco IOS router. DVTI for remote access has been available for a long time already and actually comes to gradually replace the old way of dynamic crypto maps, but as always people are hard to get out of the rut so mainly this great feature goes unnoticed.
In this specific setup I am using DVTI for hairpinning – i.e. I will connect using CIsco VPN client to the router and will tunnel ALL of my traffic through this connection, no split tunnel.
The main benefit of DVTI here is that using DVTI interface I can assign it ip nat inside and router will take care of NAT translating my traffic when sending it clear text to the Internet.
As always you can watch all my videos on Vimeo – vimeo.com/yurisk.info, also you can download there videos as files.
Reference on Cisco: DVTI on CIsco.com

Encrypting preshared keys stored on the cisco IOS router

You never know where your router may end up . It may be RMA’ed without proper wiping the configuration first, it may be plain simple stolen. In any of these or other unfortunate cases the last thing you would want is for the attacker get passwords or other security information stored on the router.
One piece of such information is preshared key(s) , that by default are stored in clear text.
To address this potential threat Cisco, starting IOS 12.3, provide AES encryption feature on IOS routers to encrypt the stored preshared keys. In video below I recorded you can see the walkthrough to enable and manage this security feature.
Enjoy. As always suggestions, critics, comments are welcome .
NB – Narration is in English.

Cisco – how to schedule an unattended reload with EEM

Good evening everyone,
Today a colleague of mine asked if I had a ready-to-use template to schedule a reload of Cisco IOS router .
–    “Of course, piece of cake, there should be millions of hits on it in Google” , was my thought. So, after 30 minutes of searching the mighty G and being surprised to have found nothing I dragged from my notes this recipe dated 2007 but still valid as ever.
NB Word of warning to those trying to do it with built in KRON service of IOS – rebooting a router requires to answer  “yes” at the CLI prompt and therefore will NOT work with KRON, only EEM can do it.
IOS used and tested – IOS 12.4T

conf t
Edge(config)#event manager applet ReloadMe
Edge(config-applet)#event timer cron name ReloadMe cron-entry “05 09 * * *”
Edge(config-applet)#action 33 reload
wr mem

This will reload router every day at 09:05, for other formats see man page for cron in Linux

sh run
event manager applet ReloadMe
event timer cron name ReloadMe cron-entry “05 09 * * *”
action 33 reload

How to separate inbound and outbound data graphs in Nfsen Netflow tool

As I said already ( here and here ) for gathering Netflow data, especially with security in mind, I deem Nfsen/nfdump to be the best. And with some easy 2-minutes tweaking I can always make it do exactly what I want.
By default when you configure Cisco to export both ingress and egress Netflow data from the interface Nfdump/Nfsen will accept and process it fine BUT … will show it on the same timeline with the same color and so overlapping over each other. That means you will see only the largest values. To fix it you create additional (from Live) profile with separate Channels, each representing direction of the traffic – inbound or outbound. Then for each channel you set appropriate filter – IN for incoming traffic , OUT for outgoing traffic (all respective to the interface being monitored), followed by SNMP ifIndex of the interface in the router. Picture is worth 1024 words they say , so see below screenshots how I did it for one of my clients.

Nfsen custom profile with channels

Nfsen custom profile with channels

Nfsen custom profile with channels

Nfsen custom profile with channels


Cisco Netflow performance data

Not much of a post but link to the Cisco site stating how much Netflow loads the Cisco routers:
I, personally, do a lot of Netflow monitoring and can say that on unloaded routers , passing 2-5 mbits/sec of traffic, the additional load will be some 1-2% of CPU cycles. For the most loaded pair of routers I do monitoring for , two Cisco 2800 passing about 70 Mbits/sec of traffic and creating about 900 Mbytes of Netflow data a day each, enabling Netflow added 8% of CPU load and they cope with it perfectly well.

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