Looking for:
Dhcputil.exe download |
Using DHCPUtil to Test DHCP Server Configuration for Lync Phone Edition.DHCP Option 120
This document describes the role of DHCP in Lync server discovery process, and how to perform the required configuration. DHCP is used for following purposes by Lync clients IP discovery — NOT discussed in this document. This topic is the subject of discussion in this document.
It can only do DHCP. Let us look at the two scenarios in more details. When an Aries phone boots up for the first time and it is not paired to Lync Client installed on a computer through USB connection, the following things would happen roughly Parameter request list option 55 — Option , Option More on this later. The client can choose any valid reply which contains the values for requested DHCP options and Option contains the location of one or more Lync Servers registrars.
Option 43 contains the location of Certificate Provisioning Web Service. This web service will be used by the client to get a certificate, which can then be used to authenticate against other Lync Servers using TLS-DSK for SIP Servers and message-based certificate authentication for web services.
Since the Aries phone will have no trusted root certificate by default except for some well-known public Certificate Authorities like Verisign , it cannot connect to Lync Servers over SSL. This communication would happen over plain HTTP. Please note that this can happen only within the corporate network.
This function for getting the root chains is exposed only on internal Lync Web Services. Once root cert chains for Lync Servers are trusted, the phone client will then connect to the Certificate Provisioning Web Service again this time over secure http , and authenticate using the user provided phone number and PIN. If the authentication is successful, the client will invoke two functions;-. GetAndPublishCert — this function will issue a certificate to the authenticated user for the current device.
At this point the sign-in is successful. If there are Lync Servers like Branch Office Appliance within the branch, then it is desirable for the clients to be able to discover and connect to these servers even during WAN outage. This discovery can happen by using DHCP. Once the client detects that it can no longer talk to the registrar that it has previously talked to, it will initiate the full discovery process. The client would then use the retrieved value option again and try to connect to it.
If the DHCP configuration is correct, then the server would be inside the branch office. Lync Clients maintain an internal mapping between FQDN and IP address, so even in case of failure of host name resolution, the client will be able to connect to appropriate server assuming that the client as connected to the server at least once before, which would always be the case except in some very remote corner cases.
The documentation can be found in RFC and Options 43 vendor specific information , 55 parameter request list and 60 vendor class identifier are defined in RFC Option 55 is used by the client to ask the DHCP Server for values of certain options in our case and Option 60 is used by the client to convey the vendor for which the value for option 43 is being requested. Option 43 is a complicated option, in the sense that it internally contains multiple sub-options, and can also have many values.
Effective value for option 43 or the value that the DHCP Server will send to the client depends on the vendor class id. The use case for this component is very small branches which have no DHCP Servers and minimal server administration.
Ask for Option or 43 using option 55 — parameter request list. This is the correct time to gain a little understanding of how DHCP Packets reach from the client to server and back. The problem with broadcasts is that in general they are not forwarded by routers. So, broadcasts from one subnet would typically not reach any other subnet.
Either way, what they do is Receive the broadcast request from client. Receive response from the server. Now, let us move on to the deployment strategies. There are two scenarios that need to be addressed The reasons being Re-configuration of relay agents : Using Lync DHCP Component would require re-configuration of all the Bootp relay agents to relay packets to a new server. Increase in network load: Using Lync DHCP Component would mean that same network packets are sent to one more server, and most of the time needlessly because Lync DHCP Component does not participate in IP acquisition process, so most of the packets which comes its way would be junk.
Increase in load on Lync Servers : DHCP Component would add one more responsibility to the Lync Servers, which can potentially affect performance of their core functionalities. Their DHCP Servers might not be configurable, thereby making it impossible to configure the options that are required for Lync Clients.
Relay agent re-configuration minimal or unnecessary: Depending on the size of a branch office, all the devices might be in the same sub-net, this making relay agent re-configuration unnecessary. If there are multiple sub-nets, then their number is likely very small, so re-configuration is possible.
DHCPUtil will now be examined in detail. Generating the values for option and DHCPUtil ships in the installation media, and is also part of the resource kit tools. Installation media contains the bit version, which should work on all platforms. The resource kit tool would only contain bit version unless bit versions of resource kit tools are also made available.
It might also be because of load balancer configuration- web traffic might be load-balanced differently from sip traffic and therefore the FQDNs of sip server and web servers are different. The value should be location of the Lync web server corresponding to Lync Sip Server specified in the first parameter. The formula is This might come in handy when the URL calculated using the formula above will not yield correct value. Option The first two values sip server and the URL for CertProv Service just emit the values that would be used for calculation.
The value for option is emitted next. This value is binary string in hex-encoded format, and can be used as is for DHCP Server configuration. Vendor Class Identifier is the next output. Please review the explanation for option 43 in a previous section according to which option 43 is a set of sub-options, and the sub-options have meaning only for a particular vendor class id.
All sub-options for option 43 are also binary string in hex-encoded format, and can be used as is for DHCP Server configuration. Sub-option 2 is the URL scheme https in this case. Sub-option 5 is the relative path of Certificate Provisioning Service.
Possible steps are It delegates that responsibility to a script which can be changed to suit the enterprise need. Once it calculates the values for various options, DHCPUtil just passes these values to the script, which can then take appropriate action.
Here is what the script contains The first three commands just cleanup a DHCP Server, so that values for various options can be set properly. If the script is invoked in cleanup mode, then it takes no further action. Otherwise, it first creates the definition for option and then sets the supplied value for it.
More on supplying a value later. After that, it moves on to set the various sub-options for option 43 one-by-one.
You can notice that these sub-options are created for Vendor that was created by the script. Only the last option RunConfigScript is new here others were detailed before. What happens when this option is specified is that DHCPUtil generates the values for option and 43, and then passes the values to the configuration script. If a valid file path is specified, then that file is executed. This file can be anything — a script, or an executable. The parameters passed to the script are specified in order they are passed Mode: Possible values are Cleanup and Configure.
Value of the Vendor Class Identifier. Value of option Value of sub-option 1 for option Value of sub-option 2 for option Value of sub-option 3 for option Value of sub-option 4 for option Value of sub-option 5 for option Admins can use this documentation to come up with custom scripts that can do whatever they want. It an appropriate response is received, the retrieved values are shown as result.
Please note that this may require appropriate exclusions in the firewall. It should ideally be run on a machine which is served by the DHCP Server whose configuration is to be tested. To enable exclusions, run the following commands from an elevated command prompt:. Once you are done, you can run the following commands from an elevated command prompt to remove the exclusions:.
Sample Output:. Starting Discovery.
No comments:
Post a Comment