Exercise 1.1: LER and Granularity

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In an MPLS network, the LERs serve as quality of service (QoS) decision points. One method to establish these policies is to use the port numbers in Layer 4 of a packet The tradeoffs in establishing these policies come from how much granularity is needed versus how manageable the configurations and tables are.

In the first example, we have created an MPLS LER table with three criteria: rules on IP address only, IP and protocol number, and IP protocol and port number.

Additionally, we have established routing paths A-Z, and we call them forward equivalence classes, or FECs. The FEC A paths are the highest-quality paths, and the FEC Z paths are the lowest-quality paths.

The policies use the port numbers to place traffic on particular paths. Port numbers are:

20/21 FTP, 25 E-Mail, 80 HTTP, 443 HTTPS, 520 Routing

1. 

Examine the table and determine the category (IP, IP-protocol, IP-protocol and port) with the most entries.

2. 

In Table 1.1, using the IP, protocol, and port number sections, how would HTTPS be handled in relationship to HTTP?

Table 1.1: MPLS LER Table

Sort and Classify by	Source IP	Target IP	DiffSer	Protocol # (Hex)	Port #	Label Out	Port Out	Inst	Fec
IP Only	192.168.10.0-255	40.5.0.0-255	All	All	All	200	A	Push	X
IP, Protocol	192.168.10.0-255	40.5.0.0-255	None	6	All	10	A	Push	A
IP, Protocol	192.168.10.0-255	40.5.0.0-255	None	11	All	20	A	Push	B
IP, Protocol, port	192.168.10.0-255	40.5.0.0-255	None	1	All	30	A	Push	C
IP, Protocol, port	192.168.10.0-255	40.5.0.0-255	None	6	20	10	A	Push	A
IP, Protocol, port	192.168.10.0-255	40.5.0.0-255	None	6	21	10	A	Push	A
IP, Protocol, port	192.168.10.0-255	40.5.0.0-255	None	6	80	20	C	Push	B
IP, Protocol, port	192.168.10.0-255	40.5.0.0-255	None	6	443	10	A	Push	A
IP, Protocol, port	192.168.10.0-255	40.5.0.0-255	None	6	25	10	A	Push	A
IP, Protocol, port	192.168.10.0-255	40.5.0.0-255	None	11	53	30	C	Push	A
IP, Protocol, port	192.168.10.0-255	40.5.0.0-255	None	11	69	200	A	Push	A
IP, Protocol, port	192.168.10.0-255	40.5.0.0-255	None	11	520	200	C	Push	X

3. 

Describe a circumstance in which HTTPS should be handled differently from HTTP.

4. 

What FEC classification is given to routing?

5. 

How could giving the above classification to routing become a problem?

Answers

1.	The table with the most entries is the table that sorts by IP address, protocol number, and port number.
2.	HTTPS uses FEC A, whereas HTTP uses FEC B. Since HTTPS could produce revenue and is secure it has a higher priority.
3.	HTTPS is given a higher priority because it offers the opportunity for revenue.
4.	Routing is classified as FEC Z (which is the lowest FEC rating).
5.	Routing and label distribution should be given the highest priority in the network; otherwise, packets could be misrouted.

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