ARP, RARP, PPTP, DHCP, DVMRP, ICMP

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Address Resolution Protocol / Reverse Address Resolution Protocol - to initialize the use of Internet addressing on an Ethernet or other network that uses its own media access control (MAC). ARP allows a host to communicate with other hosts when only the Internet address of its neighbors is known. Before using IP, the host sends a broadcast ARP request containing the Internet address of the desired destination system.

16		32
Hardware Type		Protocol Type
HLen (8)	Plen (8)	Operation
Sender Hardware Address
Sender Protocol Address
Target Hardware Address
Target Protocol Address
Structure of the ARP / RARP header in 32 bit lines.

DCAP

Data Link Switching Client Access Protocol - is used between workstations and routers to transport SNA / NetBIOS traffic over TCP sessions. The DCAP packet header is used to identify the message type and length of the frame. This is a general purpose header used for each frame that is passed between the DCAP server and the clien.

8	16
Protocol ID / Version Number	Message Type
Packet Length
Structure of the DCAP header in 32 bit lines.

ATMP

Ascend Tunnel Management Protocol - is a protocol currently being used in Ascend Communication products to allow dial-in client software to obtain virtual presence on a user's home network from remote locations. A user calls into a remote NAS but instead of using an address belonging to a network directly supported by the NAS, the client software uses an address belonging to the user's 'Home Network'. This address can be either provided by the client software or assigned from a pool of addresses from the Home Network address space. In either case, this address belongs to the Home Network and therefore special routing considerations are required in order to route packets to and from these clients. A tunnel between the NAS and a special 'Home Agent' (HA) located on the Home Network is used to carry data to and from the client.


Version	Message type	Identifier
Structure of the ATMP packet in 32 bit line.

L2F

Layer 2 Forwarding protocol - permits the tunneling of the link layer of higher layer protocols. Using such tunnels it is possible to divorce the location of the initial dial-up server from the location at which the dial-up protocol connection is terminated and access to the network provided.

Ver

Protocol

Sequence (opt)

Multiplex ID

Client ID

Length

Payload offset

Packet key (optional)

Payload

Checksum

Structure of the L2F packet in 32 bit lines.

L2TP

Layer 2 Tunneling protocol - is used for integrating multi-protocol dial-up services into existing Internet Service Providers Point of Presence (hereafter referred to as ISP and POP, respectively). This protocol may also be used to solve the 'multilink hunt-group splitting' problem. Multilink PPP, often used to aggregate ISDN B channels, requires that all channels composing a multilink bundle be grouped at a single Network Access Server (NAS). Because L2TP makes a PPP session appear at a location other than the physical point at which the session was physically received, it can be used to make all channels appear at a single NAS, allowing for a multilink operation even when the physical calls are spread across distinct physical NASs.

Ver

Length

Tunnel ID

SESSION ID

AVP (Bytes +)

Structure of the L2TP packet in 32 bit lines.

Data messages have two additional fields before the AVP as follows:

16	32
Offset size	Offset pad
Structure of the L2TP additional fields in 32 bit lines.

The AVP (Attribute-Value Pair) is a uniform method used for encoding message types and bodies throughout L2TP. The format of the AVP is given below:

6						16	32
M	H	O	O	O	O	Overall length	Vendor ID
Attribute							Value
Value
Structure of the L2TP AVP header in 32 bit lines.

PPTP

Point to Point Tunneling Protocol - allows PPP to be channeled through an IP network. It uses a client-server architecture to decouple functions which exist in current Network Access Servers and support Virtual Private Networks. It specifies a call-control and management protocol which allows the server to control access for dial-in circuit switched calls originating from a PSTN or ISDN, or to initiate outbound circuit switched connections. PPTP uses a GRE-like (Generic Routing Encapsulation) mechanism to provide a flow- and congestion-controlled encapsulated datagram service for carrying PPP packets.

16	32
Length	PPTP message type
Magic cookie
Control message type	Reserved
Structure of the PPTP header in 32 bit lines.

DHCP

Dynamic Host Configuration Protocol - provides Internet hosts with configuration parameters. DHCP is an extension of BOOTP. DHCP consists of two components: a protocol for delivering host-specific configuration parameters from a DHCP server to a host and a mechanism for allocation of network addresses to hosts.

8	16	24	32
Op	Htype	Hlen	Hops
Xid (4 Bytes)
Secs (2 Bytes)		Flags (2 Bytes)
Ciaddr (4 Bytes)
Yiaddr (4 Bytes)
Siaddr (4 Bytes)
Giaddr (4 Bytes)
Chaddr (16 Bytes) : :
Structure of the DHCP header in 32 bit lines.

DVMRP

Distance Vector Multicast Routing Protocol - is an Internet routing protocol that provides an efficient mechanism for connectionless datagram delivery to a group of hosts across an internetwork. It is a distributed protocol that dynamically generates IP multicast delivery trees using a technique called Reverse Path Multicasting DVMRP combines many of the features of RIP with the Truncated Reverse Path Broadcasting (TRPB) algorithm. DVMRP is developed based upon RIP because an implementation was available and distance vector algorithms are simple, as compared to link-state algorithms. In addition, to allow experiments to traverse networks that do not support multicasting, a mechanism called tunneling was developed.

8	16	24	32
Type	Code	Checksum
Reserved		Min version	Maj version
Structure of the DVMRP header in 32 bit lines.

ICMP

Internet Control Message Protocol - messages which generally contain information about routing difficulties with IP datagrams or simple exchanges such as time-stamp or echo transactions.

8	16	32
Type	Code	Checksum
Identifier		Sequence number
Address mask
Structure of the ICMP header in 32 bit lines.

ICMPv6

Internet Control Message Protocol version 6 - was revised during the definition of IPv6. In addition, the multicast control functions of the IPv4 Group Membership Protocol (IGMP) are now incorporated with the ICMPv6.

8	16	32
Type	Code	Checksum
Structure of the ICMPv6 header in 32 bit lines.

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