network protocols handbook.pdf

78Protocols GuideTCP/IP - Network Layer ProtocolsProtocol NameVRRP: Virtual Router RedundancyProtocolProtocol DescriptionVirtual Router Dedundancy Protocol (VRRP) specifies an electionprotocol that dynamically assigns responsibility for a virtualrouter to one of the VRRP routers on a LAN. The VRRP routercontrolling the IP address(es) associated with a virtual routeris called the Master, and forwards packets sent to these IP addresses.The election process provides dynamic fail over in theforwarding responsibility should the Master become unavailable.This allows any of the virtual router IP addresses on theLAN to be used as the default first hop router by end-hosts.The advantage of using VRRP is a higher availability defaultpath without requiring configuration of dynamic routing or routerdiscovery protocols on every end-host. VRRP packets are sentencapsulated in IP packets.Using VRRP, a virtual IP address can be specified manually orwith Dynamic Host Configuration Protocol (DHCP) as a default.A virtual IP address is shared among the routers, with one designatedas the master router and the others as backups. In case,the master fails, the virtual IP address is mapped to a backuprouter’s IP address. (This backup becomes the master router.)VRRP can also be used for load balancing. VRRP is part of bothIPv4 and IPv6.Protocol Structure4 8 16 24 32bitVersion Type Virtual Rtr ID Priority Count IP AddrsAuth Type Advet Int ChecksumIP Address 1…….IP Address nAuthentication Data 1Authentication Data 2• Auth Type -- Identifies the authentication method beingutilized.• Advertisement Interval -- Indicates the time interval(in seconds) between advertisements.• Checksum – 16 bit field used to detect data corruptionin the VRRP message.• IP Address(es) -- One or more IP addresses that areassociated with the virtual router. The number of addressesincluded is specified in the “Count IP Addrs”field. These fields are used for troubleshooting misconfiguredrouters.• Authentication Data -- The authentication string iscurrently only utilized for simple text authentication,similar to the simple text authentication found in theOpen Shortest Path First routing protocol (OSPF). Itis up to 8 characters of plain text.Related protocolsIP, IPv6, DHCP, TCPSponsor SourceVRRP is defined by IETF (http://www.ietf.org) RFC2338.Referencehttp://www.javvin.com/protocol/rfc2338.pdfVRRP Specification• Version -- The version field specifies the VRRP protocolversion of this packet. This version is version 2.• Type -- The type field specifies the type of this VRRPpacket. The only packet type defined in this versionof the protocol is: 1 ADVERTISEMENT.• Virtual Rtr ID -- The Virtual Router Identifier (VRID)field identifies the virtual router this packet is reportingstatus for.• Priority -- Specifies the sending VRRP router’s priorityfor the virtual router. VRRP routers backing up avirtual router MUST use priority values between 1 to254 (decimal).• Count IP Addresses --The number of IP addressescontained in this VRRP advertisement.