Administering Cisco QoS for IP Networks
Tweak and tune your Cisco routers for best performance with this practical guide.
TABLE OF CONTENTS Administering Cisco QoS for IP Networks
Implementing Packet Types
Now that we have explored the basic components of EIGRP, let s take a moment to discuss the packet types that establish the communications between EIGRP-speaking routers.
EIGRP implements five packet types:
- Hellos Used for neighbor discovery/recovery and to acknowledge reliably sent information.
- Updates Used to inform neighbors of topology changes, or to convey routing information to a newly discovered neighbor.
- Queries Used to request routing information from neighbors when a route has become active.
- Replies Used to respond to queries.
- Requests Unused. Originally intended for use in route server applications.
All of these packets share the same packet header format shown in Figure 2.6.
Figure 2.6: EIGRP Packet Header
The particular packet type is specified in the OPcode field following the rules in Table 2.2.
| OPcode | Type |
|---|---|
| 1 | Update |
| 3 | Query |
| 4 | Reply |
| 5 | Hello |
| 6 | IPX SAP |
TLV stands for Type/Length/Value and contains the information used to share routing information. Type is specified as one of the two octet values listed in Table 2.3.
| Number | TLV Type |
|---|---|
| General TLV Types | |
| 0x0001 | EIGRP Parameters |
| 0x0003 | Sequence |
| 0x0004 | Software Version |
| 0x0005 | Next Multicast Sequence |
| IP-Specific TLV Types | |
| 0x0102 | IP Internal Routes |
| 0x0103 | IP External Routes |
| AppleTalk-Specific TLV Types | |
| 0x0202 | AppleTalk Internal Routes |
| 0x0203 | AppleTalk External Routes |
| 0x0204 | AppleTalk Cable Configuration |
| IPX-Specific TLV Types | |
| 0x0302 | IPX Internal Routes |
| 0x0303 | IPX External Routes |
Figure 2.7 gives the format of a General TLV. As you can see, this is...
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