DHCP

ENGINEERING MANAGEMENT Course EMP-5116 Issues in the Management and Operation of Communication Prepared by Student Number Submitted To KAMRUL KHAN 7025417 Dr. Serban Gheorghe Term Report (FALL 2012) December 13, 2012 The main purpose of using DHCP is to assign unique IP address to the computers in a network. This protocol is widely used by the ISPs to let their customers join the internet with less effort. It is also used by the enterprises to reduce workload and simplify the network management. (1) (2) 1. 1 History of DHCP Before DHCP was developed a protocol named Bootstrap Protocol (BOOTP) was developed for similar functionality as DHCP. Later in 1993, DHCP was introduced for the first time with the release of RFC 1531 as an extension to the BOOTP. The main reason behind extending BOOTP was that manual intervention was required to add configuration information for each client. Furthermore, BOOTP had no mechanism to reclaim disused IP addresses. Within a short period of time, DHCP became popular among the IT community. In 1997 another update of DHCP was released through RFC 2131. RFC 3315 defined the DHCPv6 specification. RFC 3633 was released with a prefix delegation mechanism for DHCPv6. RFC 3736 mechanism to provide configuration information to clients configured using stateless address auto configuration was added as an extension. (1) 1. A brief overview A database of available IP addresses and configuration information is maintained by the DHCP server. When a client requests the DHCP server for configuration information, the DHCP server checks the subnet in which DHCP client is connected, and then sends back the client with appropriate configuration information. 2 Typically IP addresses distributed to clients are assigned f or limited interval by the server. DHCP clients are responsible for renewing their IP address before that interval has expired. If they are unable to renew it by the expiration interval, they must stop using the address. Both IPv4 and IPv6 are supported by DHCP. Even if a client does not use DHCP for acquiring IP address, it can still be used to obtain other configuration information. (1) 2 2. 1 DHCP and Its operation DHCP Protocol Overview The major component of DHCP is the DHCP server and clients. Basic task of server is to assign IP address to the clients. The DHCP client makes a request to a DHCP server that may or may reside on different subnet. The server distributes IP address, subnet mask and default gateway to a host. Other configuration parameters such as name servers and netbios configuration can also be included. The IP assignment process is called â€Å"binding† or â€Å"lease†. The word â€Å"lease† is used as the client leases an IP address for a particular amount of time. This implies, after a certain period of time client must relinquish the IP address. The DHCP client side works combining six basic states. These states are: Initializing Selecting Requesting Binding Renewing Rebinding These states will be discussed in details in the next chapters of this paper. (3) 3 2. 2 DHCP Lease As discussed before DHCP lease is the process of associating IP address and client. The address leased by the client expires after certain period of time. Two timers are maintained by the client to manage this expiration process. Which are, 1. Renewing time T1 2. Rebinding Time T2 Renewing time T1 means the client will get a new lease from a server. Rebinding is the extension of lease. Typically renewing time is set to half of the renewing time. (4) 2. 3 DHCP Messages and Client States DHCP has several messages for establishing server to client communications. All DHCP instruction or updates are carried through these messages. The basic messages defined for DHCP are, DHCPDISCOVER, DHCPOFFER, DHCPREQUEST, DHCPACK, DHCPNAK, DHCPDECLINE, DHCPRELEASE, and DHCPINFORM. All these messages are effectively used during different states of DHCP. Purpose and flow of these messages in different DHCP states are discussed in the following sections. (4) 2. 3. 1 INIT The client tries to find a DHCP server by broadcasting DHCPDISCOVER message. It transitions to the SELECTING state. The server sends DHCPOFFER back to the client which is basically the choice of address and other parameters for the client. (5) 2. 3. 2 SELECTING In this state, client waits for DHCPOFFER message from any server. It selects the preferred offer and declares the selection by sending the DHCPREQUEST message. It transitions to the REQUESTING state. (5) 4 2. 3. 3 REQUESTING After sending the DHCPOFFER the client waits for the response from the server. Three different situations can occur. First, the most expected situation that, the server sends the acceptance of the request sent through DHCPACK. The client the starts the T1 and T2 timers and moves to the Bound state. Second, if the previously sent offer is no more available the server ill send a DHCPNAK message to deny the DHCPREQUEST. In this situation the client must return to the INIT state and start from the beginning. Third, server may send acceptance through DHCPACK however, the offer is no more acceptable to the client. Typically, this happens if the client finds the offered address is already been used somewhere else in the network. In this case client sends a DHCPDECLINE message and moves to the INIT state to start over. (4) 2. 3. 4 BOUND If lease assignment is successful the client goes to BOUND state. After timer T1 is expired the client sends a new DHCPREQUEST and moves to RENEWING state. 4) 2. 3. 5 RENEWING In this state client tries to extend of its lease by sending new DHCPREQUEST to the same server it took the lease from. Again three situations may be observed. First, the server may deny the request through DHCPNAK message. The client must return to INIT state and start from beginning in this situation. Second, if client does not get response from server, it will broadcast DHCPREQUEST after T2 is expired and move to the REINDING state. Third, server accepted the new request with the DHCPACK and the lease is extended. The client will again move back to BOUND state in this situation. 4) 5 2. 3. 6 REBINDING As discussed earlier, client moves to REBINDING state if T2 get expired in RENEWING state. Here, if client may get a DHCPACK response from the server if the request is approved. The client will then return to BOUND state extending the lease. Otherwise, the client gets a DHCPNAK response which indicates the refusal of request. In this case the client needs to move to the INIT state to start from beginning. (4) 2. 3. 7 INIT-REBOOT This state is for special case. If a client can find its previous DHCP configuration right after starting up, it moves to special INIT-REBOOT state. It sends a DHCPREQUEST message immediately from where it got the previous lease requesting to use the same old address and moves to the REBOOTING state. (4) 2. 3. 8 REBOOTING In REBOOTING state, client requests the server for allowing the client to continue with the previous address. Here, again two situations may occur. First, server may accept and send DHCPACK. Client will then reset timer T1 and T2 and continue with the previous address. Second, client may get a DHCPNAK message indicating the refusal of the request. Typically this kind of situation occurs when the client is turned off for very long time. The server may assign the address to other client. And as usual the only way left for the client is to go back to the INIT state and start from the beginning. (4) 2. 4 The Finite Client State Machine Finite State Machine (FSM) is a tool or method to describe a protocol. The behavior of a protocol is described by showing all the different states a device can be in, all possible transitions between individual states, events that cause transitions, and the actions that are performed as a response of an event. 6 The FSM can be used to describe the lease life cycle from the perspective of a DHCP client. The client begins its life cycle from the initial INIT state when no lease is acquired. It then travels through different states like, renews, rebinds and/or releases its IP address. The whole process can be described graphically using the FSM method. The below figure describe the FSM of DHCP client. (5) Figure 1: DHCP Client Finite State Machine 7 3 DCHP Server Vendors and Market Overview The ever increasing number of IP devices (Network endpoints, IP telephones, virtual servers, etc. ) is the main emerging factor of IP management and DCHP server market growth. In the past, the network admins had very limited options to pick up a DHCP/DNS solution. Sometimes, they used to write their own codes to manage DHCP/DNS in their network. However, now many vendors have come up with DHCP/DNS solutions. The integrated DNS/DHCP appliancebased offerings are proved to be more attractive to the consumers. (6) 3. 1 Present Market Statistics According to the recent statistics, DHCP solutions along with DNS and IPAM (DDI) have been showing more than 20% consistent growth starting from 2009. In 2011, DDI market had an increment of 36% by generating $290 million. It is estimated that, by the end of 2012, the market will increase to $380 million with an increment of 29%. According to the statistics mentioned above it can clearly be stated that, the DDI market is promising and growing. (7) 3. 2 Market Segments In general, DDI( DNS, DHCP and IPAM) solutions can be categorized in three major segments, bundled offerings, overlay management solutions and managed services. These segments are described in the following sections. (7) 3. 2. 1 Bundled Offerings Bounded offerings are the fastest growing in DDI market. In bundled offerings, the DHCP and DNS services share an integrated database. Although, physical appliance forms are the dominating factor of bundled offerings, software or virtual services are also available. (7) 3. 2. 2 Overlay Management Solutions Overlay management solutions are free DHCP or DNS services. It is easier to deploy as it does not require replacement of DHCP/DNS infrastructure or integration with existing DNS server. It can add management capability to DNS or DHCP and IPAM functionality. (7) 8 3. 2. 3 Managed Services Managed service market is smaller comparing to other segments. According to recent statistics it is around 10% of the total spending of DDI solutions. 7) 3. 3 DDI Vendors Though DDI market is growing, some giant DDI vendors discontinued with their products due to slow revenue and other factors like increasing popularity of appliance based offerings. For example, Nortel used to be one of the market leaders in the field of DDI. However, they decided to discontinue their IP Address Domain Manager from the beginning of 2008. On the ot her hand, Infoblox and BlueCat are getting more popular with their integrated DNS/DHCP appliance based offerings. There are couple of â€Å"free DHCP solutions† available in the market. Among them, the Internet Software Consortium should be mentioned in the first place. Other than that the CMU DHCP server is also very popular (4). However, considering the market scopes and market segments it was found the commercial solutions are more promising. Therefore, in this report only the commercial solutions are briefly described. According to recent market analysis, seven companies were found to be prominent. Their overall rating based on product/service, customer feedback and business strategy is given in the chart below. (7) Figure 2 Market Scope for DDI Source: Gartner, April 2012 9 3. . 1 Alcatel-Lucent Alcatel-Lucent developed their DDI solution VitalQIP back in 1998. It has flexible deployment options with broad overlay solutions. The solution is highly capable with large enterprise network. However, some common features like the DHCP lease history is missing in VitalQIP. This can be considered as major drawback. (7) 3. 3. 2 BlueCat Networks BlueCat is a DDI pure-pla y vendor based on Toronto, Canada. They offer Adion family of integrated DNS and DHCP which can be used as an overlay to manage windows DNS and DHCP. It has strong network discovery and endpoint mapping ability. 7) 3. 3. 3 BT Diamond Diamond IP was released on 2007 by British Telecom. It is a highly scalable product. It is available through software, appliance or for virtual environment (VMWare). Diamond IP is present in all three market segment discussed before: Bundled offerings, overlay and managed services. (7) 3. 3. 4 EfficientIP EfficientIP is another pure-play DDI vendor based on France. They provide solutions as bundled or overlay. The main feature of EfficientIP is its template based architecture functionality which makes it very easy to automate the configuration and management of DNS/DHCP servers. 7) 3. 3. 5 InfoBlox InfoBlox is a California based company founded on 1999. They sell integrated DHCP/DNS solutions and overlay solutions for Microsoft Windows DHCP. Their solutions are available through appliance and virtual VMWare environment. One of the main features of InfoBlox is its grid functionality which makes the operation and management easier. (7) 10 3. 3. 6 Men & Mice Men &Mice is a Iceland based company founded at 1990. They do not sell any integrated DNS/DHCP appliance. They only sell software based overlay solutions for managing DNS/DHCP services from othe r vendors. 7) 3. 3. 7 Nixu Software A Finland based company founded on 1988. The DDI components of Nixu software are only available as software appliance. (7) 4 4. 1 Case Study: TYROLIT Delivers Resilient DNS and DHCP with BlueCat Networks Background TYROLIT is an Austria based company founded in 1919. It is one of the world's largest manufacturers of grinding, cutting, drilling dressing tools and machines for the construction industry. TYROLIT has base in 12 different countries with 4,500 employees at 27 production locations. TYROLIT’ has a