Nowadays there are some technologies which every vendor talk about. SD-WAN is very hot topic but another one is Intent Based Networking. Read more
Documentation is an extremely important rule when building a network. You will know what has been done in your network. With a good network documentation, the network support and maintenance procedures could handle the incidents in a more professional and organized way.
Without a good network documentation, there is no map, topology or information to troubleshoot your network step by step.
EIGRP in the Service Provider Networks. If you are wondering whether EIGRP (Enhanced Interior Gateway Routing Protocol) is used in the Service Provider networks, then continue to read this post.
Submarine cables carry whole Internet Traffic. I am not exaggerating. Today’s 95% of the Internet Traffic is carried over Submarine cables.
They are so important but as a network engineer how much do you know about Submarine cables ?
Istanbul/Turkey Onsite CCDE Training will be held between August 30 – September 3, 2018.
Course will be in English as usual, everyday will be between 9am – 6pm, 9 hours.
If you are replacing one technology with the other, these questions you should be asking.
How many labels for VPN in MPLS ?
My recent experience on CCDE Written Exam. Read more
3 people sent me their feedbacks after they pass February 2018 CCDE Practical/Lab exam.
Exam result was announced on May 2018 (2 to 3 months after according to new CCDE Practical exam result policy) but I couldn’t find a chance to share their results on the website.
Why Content Providers (Over the Top) don’t like Access Service Providers ?
Probably title of this post could be a ‘ Power of Access Providers ‘ or better , should be ‘ Why Some Content Providers don’t like Some Access Service Providers’. You will understand the reasons at the end of the post I promise.
I realised just now that I didn’t share the names of the people who used my CCDE resources and got their CCDE numbers recently.
Make before break and break before make. I shared many posts so far which was covering the terms used in different field of networking. This one is one of them. Also I will introduce, probably to many of you, a new terminology ‘ Break before make ‘ Read more
CCDE Salary , Cisco CCDE salary. Many people have been searching these two words on the website. Many people also have been asking to me , how much they can earn monthly if they pass CCDE practical/lab exam. Read more
CCDE Training in Istanbul on November 2017. It was 5 days , almost 50 hours training. It was very intense and the attendees got tried but enjoyed too, as you will see their feedbacks in the below video.
Is BGP RR used in EBGP ? You might think I mean IBGP , not EBGP or I mean BGP Route Server, not BGP Route Reflector but no I really mean BGP RR (Route Reflector). Read more
Many of my students have been asking whether CCDE Practical/Lab Exam Result policy is still the same. Read more
I missed writing , missed writing a post lot on the website specifically !. Because I know you are reading right now and wonder where I have been.
I just checked and seen that my last post was on October 26. More than 2 months , I didn’t share anything on the website. I wanted to come here and share something , technical or social , but believe me guys November and December 2017 was so busy from my side.
One of the activity which took my time during this period was Telecom Operator design training which I did in Kenya/Nairobi on November. Safaricom Kenya – Incumbent Telecom Operator/Internet Service Provider. Read more
MPLS protocol uses labels to forward traffic between point A and B. These labels are binded to FECs and distributed on the network by means of different protocols like (LDP, RSVP, BGP-LS, SPRING).
LDP (Label Distribution Protocol “RFC5036”) is still by far the widely used protocol among them and was developed to do label distribution unlike RSVP and BGP.
In this article we will discuss how LDP binds labels to FECs and how it distributes these labels on the network.
As stated above the main goal of LDP is to distribute labels on the network so once activated on the routers LDP will try to discover directly connected peers by sending multicast messages to UDP port number 646 but it allows for discovery of remote peers using targeted hello messages that span multiple hops for some specific use cases.
Once a peer is discovered, a TCP session is established to it using the port 646 in a way to stat the exchange of Label/FEC bindings based on the features and mode that are negotiated between the peers.
To establish LSPs, LDP relies on IGP protocols and LSPs are always following the best path to destination which means that the two protocols have to work on tandem and kept synchronized to avoid any traffic loop or blackhole situation.
Label retention mode:
Label Retention means what labels a router have to conserve for a given FEC. Should a router conserve labels coming from different routers even if are not all in the forwarding path? or should it conserve only labels from the IGP best next hop router to destination and discard the rest?
The first option is called Liberal Retention and the second option is called Conservative label retention.
To explain the difference between these two modes, let’s use the diagram below:
Assuming that all links have the same cost hence to reach Loopback 0 from R1 the path “R1″>”R2″>”R4″>”R5” will be used.
- “R5” associate “L1” label to the connected loopback interface and send it to its neighbor “R4”
- “R4” binds label “L2” and send it to both “R2” and “R3”
- “R3” binds label “L3” and send it toward “R2”
- “R2” binds label “L4” to the FEC represented by the Loopback0.
From here we can raise to points :
- R2 receive two labels to the same FEC,one from “R4” and the other from “R3”
- Each router advertises a Label to its peers and expects receiving the flow tagged with that label. This method is called downstream distribution
The first remark is about retention mode. In LDP we have to mode:
- liberal retention mode: on which “R2” will retain label from “R3” and from “R4” even if in normal circumstance the LSP will be establish through trough the short path “R1″>”R2″>”R4″>”R5” this mode is resource consumer as the router will install in the Label Information Base some labels that won’t be used immediately but in case of “R2” “R4” link failure the label will switch swap rapidly to the label received and installed from “R3” earlier to repair the LSP.
- Conservative retention mode: on which R2″ and on the reception for label “L3” from “R3” it will discard it. Which make sense in case you have to preserve resources and uses them for other processes but this method comes at cost since unwanted labels are discarded,if the link between “R2” “R4” fails the traffic will be blackholed until the reception and the installation of the Label from “R3”.
Within today network, Routers come with large memory capacity to handle a large label space so the Liberal retention mode is the widely used mode.
The second remark is about the mode of label distribution:
Based on RFC3031: ” the decision to bind a particular label L to a particular FEC F is made by the LSR which is DOWNSTREAM with respect to that binding. The downstream LSR then informs the upstream LSR of the binding. Thus, labels are “downstream-assigned”, and label bindings are distributed in the “downstream to upstream” direction ” If we apply the RFC above to our diagram when “R4” receives label “L1” to loopback 0 from “R5” it assigns a label “L2” and sends it downstream to “R3” and “R2” then R2 expect that for all traffic going to Loopback 0 be tagged with “L2” label in the incoming interface before it swaps the label to “L1” and send it upstream to “R5”. This method is called downstream allocation In the other side should “R4” send label for the Loopback0 to “R3” and “R2” (unsolicited label distribution) or only for routers ask for them (On demand label distribution)?. Having known about the unwanted blackhole situation that will be raised if the second option has been used. The vast majority of vendors prefer the first mode of label distribution. So, the label distribution mode used by LDP is called downstream unsolicited.
Microwave or Fiber which one is faster ? I will explain the faster connectivity option and some of the use cases for each, deployment considerations a bit in this post. Why latency is important for some special businesses ? Have you heard about HFT (High Frequency Trading) ? If you like the discussion points, after reading the post, share your comment, let me know it so I can write more on this subject.
Below is the CCDE Practical/Lab exam dates for 2018. Read more