These may be simple but are likely to come up again and again in studies, practice tests, and perhaps the real thing.
Name the five OSPF packet types:
Hello - Discovers neighbors/builds adjacencies
Database Description - Checks to see if databases are synchronized between neighbor routers.
Link-State request (LSR) - request a specific link state record(s) from another router
LSU - Sends the specific link state record(s) requested by the LSR
LSAck - Acknowledgment of all the above packet types
The reason OSPF needs an Ack packet is because it does not use TCP or UDP, the above packets are encapsulated directly into IP.
What does a Router do when it receives an LSU (link state update)
1. If LSA entree does not already exist: add entry to LSDB, send LSAck, Flood update to other routers, run SPF, updates routing table
2. If LSA already exists with same sequence number: ignores
3. If LSA already exists with but new has later sequence number: add entry to LSDB, send LSAck, Flood update to other routers, run SPF, updates routing table
4. If LSA already exists and new LSA has older Sequence Number: sends LSU to sender with newer update
What is a Drother?
A non-DR and non-BDR on a segment - still gets a two-way adjacency state.
How does a router verify Bi-directional communication?
Sees itself listed in Hello Packet of Neighbor
OSPF's multicast address - (KNOW THIS!!!!!, Not just for the test, but for every desktop support technician who wants to send multicast images over the first few multicast addresses!!!)
224.0.0.5 - used for hello packets
Hello and dead intervals must match to create an adjacency.
By default: hello - 10 sec / Dead - 4x hello
Once a DR and BDR have been selected, any future routers joining that segment will only form adjacencies with the DR and BDR, not any DROTHERS.
Monday, December 27, 2010
Friday, December 3, 2010
Comcast vs Level 3
Because tech blogs and twitter have EXPLODED on the subject, I thought I would add my useless two cents. For those who haven't heard, comcast is having a dispute with level 3 over whether level 3 should pay them to add more links into their comcast network.
Here are the facts.
1. Formerly Akamai (CDN - Content Delivery Network) was the primary deliverer of netflix streaming video.
2. Akamai was/is a customer of comcast and paid them for the bandwidth they used.
3. Level 3 was a carrier network that had a free agreement with comcast to trade a "relatively" equal (2:1) amount of traffic between their networks.
4. Level 3 has gotten into the CDN market.
5. Akamai lost the netflix account to limelight and Level 3, two separate CDNs
6. Level 3 communications != L3 communications
7. Level 3 expects the netflix streaming will increase the amount of traffic traveling onto comcast's network to increase to a 5:1 ratio (2.9 terabits/s increase)
8. Level 3 does not think it should have to pay, comcast does
I see this ultimatly as two businesses bickering over money, the usual, but I see two arguments, for and against.
Against Comcast:
I pay you (comcast) a lot of money to provide me 12Mb/s of whatever (legal) internet content I desire to upload or download. It is your end of the bargain to have enough bandwidth to other parts of the internet to provide that in a reliable fashion. You should be taking the money I pay you to make sure ALL your links to outside carriers will not be saturated if you expect I will desire content from that part of the internet. This has nothing to do with netflix, if comcast did not have enough bandwidth to support it's customers streaming from youtube, CNN, or something else, it should be comcast that needs to add bandwidth to let more content onto it's network, as comcast is the requester. The reason I choose to continue to pay comcast and not your competitor, is that I believe you have less over-saturation and can provide the content I want.
As a network engineer, if my end users need more bandwidth into my network from a specific entree point, isn't it my responsibility to increase that bandwidth?
Against Level 3:
You made an agreement with comcast to allow 2:1 bandwidth ingress/egress from that point of your network. By adding 2.9 Terabits/s of bandwidth, you have rendered the previous contract void and need to re-negotiate. Comcast does not wish to renew the contract without raising the price. Either pay up or find a different carrier/backbone network you can connect to which will make it's own connection with comcast.
Honestly, I don't see which is a better argument, possibly Comcast's. I really don't see that this has anything to do with "net neutrality" as Level 3 was claiming though.
Here are the facts.
1. Formerly Akamai (CDN - Content Delivery Network) was the primary deliverer of netflix streaming video.
2. Akamai was/is a customer of comcast and paid them for the bandwidth they used.
3. Level 3 was a carrier network that had a free agreement with comcast to trade a "relatively" equal (2:1) amount of traffic between their networks.
4. Level 3 has gotten into the CDN market.
5. Akamai lost the netflix account to limelight and Level 3, two separate CDNs
6. Level 3 communications != L3 communications
7. Level 3 expects the netflix streaming will increase the amount of traffic traveling onto comcast's network to increase to a 5:1 ratio (2.9 terabits/s increase)
8. Level 3 does not think it should have to pay, comcast does
I see this ultimatly as two businesses bickering over money, the usual, but I see two arguments, for and against.
Against Comcast:
I pay you (comcast) a lot of money to provide me 12Mb/s of whatever (legal) internet content I desire to upload or download. It is your end of the bargain to have enough bandwidth to other parts of the internet to provide that in a reliable fashion. You should be taking the money I pay you to make sure ALL your links to outside carriers will not be saturated if you expect I will desire content from that part of the internet. This has nothing to do with netflix, if comcast did not have enough bandwidth to support it's customers streaming from youtube, CNN, or something else, it should be comcast that needs to add bandwidth to let more content onto it's network, as comcast is the requester. The reason I choose to continue to pay comcast and not your competitor, is that I believe you have less over-saturation and can provide the content I want.
As a network engineer, if my end users need more bandwidth into my network from a specific entree point, isn't it my responsibility to increase that bandwidth?
Against Level 3:
You made an agreement with comcast to allow 2:1 bandwidth ingress/egress from that point of your network. By adding 2.9 Terabits/s of bandwidth, you have rendered the previous contract void and need to re-negotiate. Comcast does not wish to renew the contract without raising the price. Either pay up or find a different carrier/backbone network you can connect to which will make it's own connection with comcast.
Honestly, I don't see which is a better argument, possibly Comcast's. I really don't see that this has anything to do with "net neutrality" as Level 3 was claiming though.
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