Always Networks Blog - ccie

Automate loading INE configs onto Cisco CSRs using Python

I haven't posted for a while. Work has been hectic, I failed my CCIE written and lost all motivation, and many other excuses. Whilst I haven't really been studying CCIE stuff, I have been productive. I have been learning Python. I decided to automate the process of loading the INE initial configs onto my CSR routers, using a Python script, and the power of pexpect …

Read whole post...

CCIE Written Blueprint: 1.3.c Interpret packet capture

Thu 09 October 2014

This is a very short section! I didn't see the point in harping on about wireshark, I use it most days at work. And the IOS embedded packet capture was discussed in length further up the blueprint (i.e. in a previous blog post).

1.3.c Interpret packet capture

1.3.c (i) Using Wireshark trace analyzer

Packet capture can be obtained using a …

Read whole post...

CCIE Written Blueprint: 1.3.b Apply troubleshooting methodologies

Sat 04 October 2014

This is another difficult section in the blueprint to write about. I find troubleshooting techniques and methodologies to be quite personal; no two people's brains work the same way. I guess this is based on how I do things and some tips I've received from a few people over the years.

1.3.b (i) Diagnose the root cause of networking issue (analyze symptoms, identify …

Read whole post...

CCIE Written Blueprint: 1.3.a Use IOS troubleshooting tools

1.3.a Use IOS troubleshooting tools

1.3.a (i) debug, conditional debug

Debugs can be used on a wide range of functions (debug ?). Some debugs can be very noisy. Debug conditions can be set to filter out some of the noise – for example debug condition interface fa0/0 will limit the debug information to things using that interface. Undebug all does not remove …

Read whole post...

CCIE Written Blueprint: 1.2.a Evaluate proposed changes to a network

Tue 09 September 2014

As the blueprint goes, this is, in my opinion, the most vague topic to write about. It is dependent on the understanding of the topics, and how the changes will impact the existing network. I have skimmed through this really, with the intention of covering the topics in their actual topic sections. I am pretty used to evaluating impact - I seem to spend my entire …

Read whole post...

CCIE Written Blueprint: 1.1.f Explain UDP operations

Wed 20 August 2014

This topic made me think about the starvation stuff. I suppose it is pretty obvious that UDP wouldn't back off if WRED was employed, but it's something I never really thought about.

I found a few good videos on YouTube which gave some good RTP/RTCP overviews.

1.1.f (i) Starvation

TCP Starvation / UDP Dominance is experienced in times of congestion where UDP and …

Read whole post...

CCIE Written Blueprint: 1.1.e Explain TCP operations

TCP - I thought I'd glance over this section. Turns out there was some stuff I'd never heard of, such as the bandwidth delay product.

1.1.e (i) IPv4 and IPv6 PMTU

Path MTU Discovery is the process of sending increasingly larger packets with the DF bit set, until finally a ICMP Destination Unreachable (Packet too large, DF bit set) message is received. The size …

Read whole post...

CCIE Written Blueprint: 1.1.d Explain IP operations

1.1.d (i) ICMP unreachable, redirect

ICMP Unreachable

Generated by a host or gateway to indicate that the packet was discarded as the destination is unreachable. It will not be generated for multicast traffic. It is sub-divided into 15 types as follows:

Code Value Message Subtype Description
0 Network Unreachable The datagram could not be delivered to the network specified in the network ID …
Read whole post...

CCIE Written Blueprint: 1.1.c Explain general network challenges

Wed 13 August 2014

1.1.c (i) Unicast flooding

One of the main causes is asymmetric routing. This is covered in 1.1.c(iii). Useful document here: http://www.cisco.com/c/en/us/support/docs/switches/catalyst-6000-series-switches/23563-143.html

The primary impact of this is that all hosts connected in that VLAN receive the traffic. Suppose two 10gig servers are communicating, and asymmetric routing is taking …

Read whole post...

CCIE Written Blueprint: 1.1.b Identify Cisco express forwarding concepts

Sat 09 August 2014

Cisco Express Forwarding - that thing that "just works". You don't really need to know anything about it...until it stops just working. Here's my notes.

1.1.b Identify Cisco express forwarding concepts

CEF maintains its tables to facilitate the routing of packets purely in memory, with no CPU overhead.

If the CPU can’t handle the packet, it “punts” the packet to the software …

Read whole post...