CCMs and MEP types

May 032011

Continuity check message (CCM)

What is good to know? (if you are familiar with the basics, go ahead and read)

First of all. CCMs are the heartbeat of the network being monitored. By protocol description, every CCM has few important parameters: Origin (Maintenance domain and association), hello interval and status bits, sequence number and some Organization specific stuff which is irrelevant to this guide. The packet looks like this:

00000000  d4 c3 b2 a1 02 00 04 00  00 00 00 00 00 00 00 00  |ÔÃ²¡............|
00000010  ff ff 00 00 01 00 00 00  96 35 c1 4c 0d 87 05 00  |ÿÿ.......5ÁL....|
00000020  74 00 00 00 74 00 00 00  01 80 c2 00 00 31 00 a0  |t...t.....Â..1. |
00000030  12 4b 2f 30 81 00 c0 03  89 02 20 01 04 46 00 01  |.K/0..À... ..F..|
00000040  3d 88 00 01 04 02 61 31  02 03 6d 61 31 00 00 00  |=.....a1..ma1...|
00000050  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
00000080  00 00 00 00 1f 00 0c 00  a0 12 02 2b 44 d3 3f 11  |........ ..+DÓ?.|
00000090  31 8a 00 04 00 01 01 02  00 01 02 00              |1...........|

If you are interested in the details, get the packet and dissect it in Wireshark.

Second. CCMs are transmitted between MEPs. By seeing each other’s CCMs the MEPs establish connectivity. There are however some important prerequisites.

MEPs in different domains do not connect to each other, no matter what.
MEPs in different associations do not connect to each other, no matter what.
MEPs with different hello intervals do not connect to each other, no matter what.

Another important thing. If you have association named MA1 for monitoring VPLS service and association MA2 monitoring VLAN with id 300, you can’t have CFM entities connected between them. No matter the VPLS could label and carry over packets with VLAN tag 300 in Its topology.

Another important thing is the Domain level:

---------- CCM level 7 --------------------->
---------- CCM level 5 ------> MEP level 5
---------- CCM level 1 ------X

MEPs filter all lower level CCMs, MEPs process all same level CCMs and MEPs pass untouched all higher level CCMs. This filtering logic is important. If you take a look in the diagram from the previous tutorial page, you will see, that Level 7 domain should not be stopped at any point if we are going to monitor it. And provider or operator domains should not flood CCM packets outside their respective End Points. This logic applies to all kinds of CFM monitored services and VLANs, and It also provides some security and less control traffic over the whole network.

Fourth. You should never forget the MEPs have direction and different behavior when they are facing UP or DOWN (respectively IN or OUT). The diagram below is created for easier understanding when I did OAM CFM presentation for my colleagues in Telco systems. It’s a bit crude, but not hard to grasp. Basically IN and UP MEPs are the same and the words “In” and “Up” have 2 letters. OUT and DOWN MEPs are the same and the words have more than 2 letters. IN/UP MEPs are sending CCM packets in direction towards the other device ports, that are members of the same domain (a.k.a. MIPs) while the DOWN/OUT MEPs are sending CCM packets in the opposite direction. If we visualize the device as a box with 5 holes it will look like this:

Easier to understand MEP direction

The difference in terminology is because of changes that took place while this relatively new monitoring protocol was developed in the last few years and the different vendors that support it. Currently, most (if not all) vendors use the Up and Down naming for MEPs, but if you happen to buy or receive older equipment or older software version – it’s good to know “which witch is which”.

Lot more can be said about CCMs and MEPs, but all in due time. If this article is too basic for you, please look at the OAM CFM connectivity chart.

Roasted lamb

My k1tch3n Comments Off

May 022011

Roasted lamb

Yet another of the St. George’s day meals.

For this one you need:

Few vine branches. As long as your preferred cooking plate.
1 big piece of lamb meat, preferably leg
125 grams of butter
Lots of green onions
Green garlic (one stem)
Few cloves of grown garlic
2 tablespoons of ground red pepper
1 tablespoon non ground savory
ground black pepper and salt to your taste.

Preparation

The lamb leg is cleaned with warm water.

It’s salted thoroughly and left to rest for 10-15 minutes to absorb part of the salt. While resting, grind the green garlic and mix with butter, red pepper, savory and black pepper. This mixture will be used to smear over the leg later.

{If the lamb meat is from a bit older animal, a good idea is to set it in few liters of water from the previous evening with sea salt or table salt poured over. Four to five tablespoons salt is enough. And If you have some Bulgarian yogurt – pour few tablespoons in the water too. It kills the smell and makes the meat easier to cook.

(We even have few words for lambs age. We call the 6 months old Shille[Шиле], while the younger brother is called Yarre, Agne or Yagne [Яре, Агне, Ягне], and oldest that are actually Rams and Sheep are called Oven[Овен] or Ovtza[Овца])}

You can use sharp knife to make small holes and to spike pieces garlic in the meat before roasting.

Get wide plate and pout about 1-2 cm water. Put the vine branches inside to form something like a grid. Put the lamb meat over the grid and pour as much water as to cover the grid. The meat is then smeared with the mix and put in the oven on medium fire (takes few hours to bake big piece of lamb).

If the meat starts to dry on top, get a spoon and pour part of the broth formed of the roasted meat juices and water around the grid. Generously.

It’s excellent with dry red wines.

Lamb rite soup (Lamb Kurban)

My k1tch3n Comments Off

May 022011

As with all rite soups, this one is made from sacrificed animal, preferably male one – bred explicitly for this purpose. We use lamb organs like spleen, kidneys and heart.

There are lots of spring herbs and red hot peppers, onions, red peppers, carrots, tomatoes, eggs and rice. But not in that order and not always all of them included. It may consist of only meat, rice and carrots with some spices. With or without hot red pepper. And sometimes with whole small mushrooms.

Kurban rite soup

It is often present on St. George’s day but also on other holidays that are connected or not to the Christian church. It’s sometimes cooked and given to the poor for good health, after someone has been sick or has suffered an accident from his relatives.

Sometimes cooked in huge pot, directly over open fire. Starting from sunrise and boiled until noon, because of the bigger quantity. It is tradition to cook large quantities and to invite all the family in one house.

Preparation.

The lamb meat, and some of the organs are diced to small pieces and put in a large pot put on medium hot plate or open fire. The foam that forms over the water is collected with wooden spoon and thrown away. When the meat is almost ready, the diced vegetables are added and boiling continues until they are cooked too.

Few eggs are mixed with cooled broth from the lamb. This mix is added in the Kurban through sieve so the end effect when the egg mix touches the boiling Kurban is like white strings. While this is done, your relative has to stir the Kurban in one direction with big wooden spoon.

Some Bulgarian cuisines also add red or brown thickening made with fried in sunflower oil ground red peppers with some flour.

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Continuity check message (CCM)

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