BASICS- ICMP REDIRECTS

Redirect, ICMP type 5, is used by routers to notify hosts of another router on the data link that should be used for a particular destination.

TOPOLOGY

——————–

———-                                   ROUTER R3——|
| Internet |                                  /                 |——PC2 10.10.10.1
———                                         /
|                                               /
ROUTER R1                            ROUTER R2
172.16.10.40|                                | 172.16.10.5

|                                 |
—————-LAN——————————–
|
|
PC1
172.16.10.1
Gateway 172.16.10.40

—————————————-
Consider above topology,where PC1 has default gatway config as 172.16.10.40 .PC1 send packet to router R1 to reach remote destination  10.10.10.1.Router R1  checks its routing table and find that next-hop to reach 10.10.10.1 is Router R2.SO now the ROuter R1 has to fwd  packet througth the same interface on which it was received.Router R1 fwd packet to Router R2 and also send ICMP redirect message to PC1.This informs about the best path to reach destination 10.10.10.1 is through Continue reading

BASICS – PROXY ARP

Its very important for routing and is enabled default in IOS.

Its method by which router made himself available to the host.How ?

|——-ROuter——|
|                            |
PC1                       PC2
IP 10.10.20.1/24      10.10.40.1/24

Consider that HostA(10.10.20.1/24) want to send traffic to HostB of diff subnet (10.10.40.1/24).
Host A neither have any default gateway configured nor it knows how to reach router.It will send arp request for 10.10.40.1,local router
when receives the request and also know how to reach subnet 10.10.40.0,will reply arp with its own hardware address.
Host A will see this reply, cache it, and send future IP packets for host B to the gateway.  The gateway will forward such packets to
host B by the usual IP routing mechanisms.  The gateway is acting as an agent for host B, which is why this technique is called “Proxy ARP”; we will refer to this as a transparent subnet gateway or ARP subnet gateway.

ARP cache entries generally shows multiple ip address are mapped to single hardware addresss ,It that case proxy arp is used and single hardware addresss is of router interface and multiple ip address is of hosts.


BASICS – ARP

How the ARP works ? Basic question but very imp to know it.

ARP is address resolution protocol,used to resolve logical IP address to physical hardware address.

ROUTER

|
|
———LAN——-
|                          |
|                          |
PC1                   PC2
10.10.10.1          10.10.10.14

Consider that PC1 want to communicate with PC2.What is the actual process to communicate b/w them ?

PC want to sent traffic to PC2 ,it has got layer 3 address for source(10.10.10.1) and also destination (10.10.10.14).
It will move from upper layer down to lower layer 2 i.e data link layer.Layer 2 need to have source and destination MAC
address information to process further.PC1 has layer 3 information for source and destination but no layer 2 information for destination .
Here comes the saviour known as ARP .PC1 will send broadcast into the LAN asking that whoever owns IP 10.10.10.14 respond with its mac address.

The broadcast packet will have following info.
Source Ip             : 10.10.10.1
Destination IP      : 10.10.10.14
Source MAC        : MAC Continue reading

On Policy in the Data Center: Comparing OpenStack policy efforts

(This post was written by Tim Hinrichs and Scott Lowe, with contributions from Pierre Ettori, Aaron Rosen, and Peter Balland.)

In the first two parts of this blog series we discussed the problem of policy in the data center and the features that differentiate solutions to that problem. In this post, we give a high-level overview of several policy efforts within OpenStack.

Remember that a policy is a description of how (some part of) the data center ought to behave, a service is any component in the data center that has an API, and a policy system is designed to manage some combination of past, present, and future policy violations (auditing, monitoring, and enforcement, respectively).

The overview of OpenStack policy efforts talks about the features we identified in part 2 of this blog series. To recap, those features are:

  • Policy language: how expressive is the language, is the language restricted to certain domains, what features (e.g. exceptions) does it support?
  • Policy sources: what are the sources of policy, how do different sources of policy interact, how are conflicts dealt with?
  • Services: which other data center services can be leveraged and how?
  • Actions: what does the system do once Continue reading

Making better use of libvirt hooks

Libvirtd includes handy hooks for doing management work at various phases in the lifecycle of the libvirt daemon, attached networks, and virtual machines. I've been using these hooks for various things and have found them particularly useful for management of short-lived Linux containers. Some of my use cases for these hooks include:
  • changing network policy
  • instantiating named routing tables
  • creating ramdisks for use by containers 
  • pre-loading data before container startup
  • archiving interesting data at container shutdown 
  • purging data at container destruction

Here's how the hooks work on a system with RedHat lineage:

The hook scripts live in /etc/libvirt/hooks. The scripts are named according to their purpose. I'm focusing right now on the LXC hook which is named /etc/libvirt/hooks/lxc. Note that neither the directory, nor the scripts exist by default.

The lxc script is called several times in each container's lifecycle, and is passed arguments that specify the libvirt domain id and the lifecycle phase. During startup and shutdown of one of my LXC systems, the script gets called five times, like this:

 /etc/libvirt/hooks/lxc MyAwesomeContainer prepare begin -  
 /etc/libvirt/hooks/lxc MyAwesomeContainer start begin -  
 /etc/libvirt/hooks/lxc MyAwesomeContainer started begin -  
 /etc/libvirt/hooks/lxc MyAwesomeContainer stopped end -  
 /etc/libvirt/hooks/lxc MyAwesomeContainer release end -

In addition to having those Continue reading

Community Show – Killing the Spanning Tree with SPB,TRILL,Fabricpath from Anthony Sequeira and Orhan Ergun

[player] No country for old men !!. This week in the Orhan Show,  Anthony Sequeira and Orhan Ergun are talking about spanning tree , its drawbacks, spanning tree modes, technologies which can eliminate the spanning tree’s drawbacks or completely do not use it. Orhan recommends all audience to read  this blog post about spanning tree […]

The post Community Show – Killing the Spanning Tree with SPB,TRILL,Fabricpath from Anthony Sequeira and Orhan Ergun appeared first on Packet Pushers.

Community Show – Killing the Spanning Tree with Anthony Sequeira and Orhan Ergun

No country for old men !!. This week in the Orhan Show,  Anthony Sequeira and Orhan Ergun are talking about spanning tree , its drawbacks, spanning tree modes, technologies which can eliminate the spanning tree’s drawbacks or completely do not use it. Orhan recommends all audience to read  this blog post about spanning tree which […]

Author information

Orhan Ergun

Orhan Ergun, CCIE, CCDE, is a network architect mostly focused on service providers, data centers, virtualization and security.

He has more than 10 years in IT, and has worked on many network design and deployment projects.

In addition, Orhan is a:

Blogger at Network Computing.
Blogger and podcaster at Packet Pushers.
Manager of Google CCDE Group.
On Twitter @OrhanErgunCCDE

The post Community Show – Killing the Spanning Tree with Anthony Sequeira and Orhan Ergun appeared first on Packet Pushers Podcast and was written by Orhan Ergun.

Network Automation with Python, Ansible, and Twitter Integration

Last month I wrote about using the Cisco Nexus NX-API to extract stats from a Nexus switch while using Ansible.  For some reason, last night I finally went on to tackle how to integrate with the Twitter API and then integrated the two together.  Integrating with Twitter has always been top of mind, but just put it on the back burner.  Funny enough though, it was a pretty quick integration thanks to the great people at Google.
What am I talking about?

In the code I pushed last month, I created an Ansible playbook that pulls interface stats from a Nexus 9000 (or any other Nexus device supporting NX-API) and then creates a template report for those stats.  It was pretty vanilla, nothing fancy about it.

There have been integrations with other social platforms, but to be honest, the one that has been stuck in my brain is Hubot that is used at GitHub.  Several months back I remember hearing about Hubot for the second or third time while listening to the Cloudcast podcast with Mark Imbriaco (just before he went to Digital Ocean).  It is amazing to see what can be done Continue reading

Automating a Multi-Action Security Workflow with VMware NSX

This post was written by VMware’s John Dias, (VCP-DCV), Sr. Systems Engineer, Cloud Management Solutions Engineering Team, and Hadar Freehling, Security & Compliance Systems Engineer Specialist

***

Through a joint effort with Hadar Freehling, one of my esteemed peers here at VMware, we co-developed a proof-of-concept workflow for a network security use case.  Hadar created a short video showing and explaining the use case, but in summary this is a workflow that reacts to and remediates a security issue flagged by third-party integration with VMware NSX. In the video, TrendMicro is used but it could be any other partner integration with vShield Endpoint.

Here’s what happens:

  • A virus is detected on a VM and is quarantined by the AV solution
  • The AV solution tags the VM with an NSX security tag
  • VMware NSX places the VM in a new Security Group, whose network policies steer all VM traffic through an intrusion prevention system (IPS)
  • vCenter Orchestrator (vCO) monitors the security group for changes and when a VM is added
    • a snapshot of the VM is taken for forensic purposes
    • a vSpan session (RSPAN) is set up on the Distributed Virtual Switch to begin capturing inbound/outbound traffic on the VM
    • once the Continue reading

Nontraditional network integrations

If you listen to the chatter around the network industry, you are starting to see a lot more discussion about integration. While particularly clueful individuals have been hip to the fact for awhile, it seems the industry at large is just awakening to the idea that the network does not exist in isolation. Put differently, the idea that the network can be oblivious to everything around it (and they to the network) is losing steam as orchestration frameworks like OpenStack take deeper root.

Having glue between the major infrastructure components is critical to having seamless operation across all the resources required to satisfy an application or tenant workload. But there is additional (potentially greater!) advantage to be had by performing some less traditional integrations.

Where do integrations matter?

There are two primary reasons to have integrated infrastructure: to cut down on time and to cut down on mistakes. Integration is almost always in support of automation. Depending on the exact integration, that automation is in support of making things faster and cheaper, or in making things less prone to Layer 8 issues.

The point here is that integration is rarely done just for the sake of integration. Companies need Continue reading

The History of Open

Everybody is talking about “open” this or that – from Cisco making claims to new companies embracing open source code as a means of developing or accelerating their go-to-market strategies. But what does “open” really mean?

One challenge in using a broad and you might say amorphous term like open is that it can lead to confusion or a negative first impression that “this is just marketing.” To get some perspective, let’s look back a bit and see how we got to this point of open and what the original intent was.

Open systems are computer systems that provide some combination of interoperability, portability, and open software standards. (“Open” can also refer to specific installations that are configured to allow unrestricted access by people and/or other computers; this article does not discuss that meaning.)

The term “open” was popularized in the early 1980s, mainly to describe systems based on Unix, especially in contrast to the more entrenched mainframes, minicomputers, and engineering workstations in use at that time. Unlike older legacy systems, the newer generation of Unix systems featured standardized programming interfaces and peripheral interconnects. Third party development of hardware and software was Continue reading

OpenDaylight in the Enterprise: OpenFlow and NETCONF in the right places

When using Open Daylight (ODL), two open standards for configuration are OpenFlow & NETCONF. Which is the better choice ? Is there an option for both ? A use case on when to use OpenFlow and NETCONF protocols in the Enterprise by using the best features of each protocol.

The post OpenDaylight in the Enterprise: OpenFlow and NETCONF in the right places appeared first on EtherealMind.

How We Filter Information About IT Products

The amount of information to be found out about tech products is astonishing. Anything you’d like to know about virtually any product is a Google search away. The hits you’ll get back are loaded with information, some useful and some…less useful. I am awash in data to ingest each and every day. I […]

Close to the wire: How route analytics can help prevent BGP-caused outages

Close to the wire: How route analytics can help prevent BGP-caused outages

by Brian Boyko, Contributor - September 16, 2014

At around 3:00 a.m. Eastern Daylight Time on August 13th, Internet users started reporting slow connectivity and intermediate outages. This impacted many large networks and hosting providers including eBay, Comcast, and Time-Warner.

The problem was that some older Cisco routers have a default limit of 512k border gateway protocol (BGP) routing entries in their TCAM memory. Normally, routing tables typically have around 500k entries, so there’s a little bit of a buffer. But BGP prefix aggregation for a major service provider’s systems temporarily failed. The service provider quickly fixed the problem on their end, but not before 15,000 new prefixes were sent to the global routing table, surpassing that 512k limit. 

There is a work-around for these routers to increase the maximum size for the routing tables, but one has to wonder why these routers were running so close to maximum to begin with. In short, there is clearly a need for a larger margin of error. 

The August 13th event highlights one of the reasons that route analytics are more important than ever. With the visibility Continue reading

Network Monitoring Videos from NFD8

In yesterday’s post (Network Monitoring – So Many Choices), I neglected to link to the videos from Networking Field Day 8 covering the network monitoring portions of the presentations from Gigamon, Pluribus and Big Switch. So rather than go back … Continue reading →

If you liked this post, please do click through to the source at Network Monitoring Videos from NFD8 and give me a share/like. Thank you!

Why is Lync The Killer SDN Application?

lync-logo

The key to showing the promise of SDN is to find a real-world application to showcase capabilities.  I recently wrote about using SDN to slice education networks.  But this is just one idea.  When it comes to real promise, you have to shelve the approach and trot out a name.  People have to know that SDN will help them fix something on their network or optimize an troublesome program.  And it appears that application is Microsoft Lync.

MIssing Lync

Microsoft Lync (neè Microsoft Office Communicator) is a software application designed to facilitate communications.  It includes voice calling capability, instant messaging, and collaboration tools.  The voice part is particularly appealing to small businesses.  With a Microsoft Office 365 for Business subscription, you gain access to Lync.  That means introducing a voice soft client to your users.  And if it’s available, people are going to use it.

As a former voice engineer, I can tell you that soft clients are a bit of a pain to configure.  They have their own way of doing things.  Especially when Quality of Service (QoS) is involved.  In the past, tagging soft client voice packets with Cisco Jabber required setting cluster-wide parameters for all clients.  It Continue reading

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