Download - DHCP Failover Hot

8/18/2019 DHCP Failover Hot

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to be able to rene! e.isting IP address leases as !ell as give out ne! IP address leases to clients !hore#uest a ne! lease% For the later scenario leasing ne! IP addresses to clients the standby serverneeds a "ree IP address pool available to it "rom !hich it can give out ne! leases% +he standby server!ill ta&e over the "ree IP address pool o" the active server only a"ter it transitions into Partner Do!nstate "rom Communicated Interrupted state and a time period o" MC,+ 'Ma.imum Client ,ead +ime)has e.pired% +his is as per theDHCP "ailover protocol% +o enable the standby server to serve ne! IPaddress leases to clients during this interim period - i%e% till it transitions to Partner Do!n and ta&es

over the entire "ree IP address pool o" a scope a percentage o" "ree IP address pool needs to beavailable to standby server% +his can be provided by the con$guration parameter reserve addresspercentage%

+he percentage o" addresses reserved "or the hot standby server can be con$gured "or a "ailoverrelationship con$gured "or hot standby mode% Free IP addresses in proportion to the percentage valuecon$gured !ould be assigned to the hot standby server% I" address reserve percentage is set to noaddresses !ill be reserved "or the hot standby server and ne! client leases cannot be granted by thehot standby server in case o" outage o" active server% +he de"ault value "or reserve address percentageis 57% Since the reserve address percentage is meant "or an interim period as discussed above thevalue chosen "or it can typically be small '5-87)%

Figure 1: Creating a Failover Relation in Hot Standby Mode

http://tools.ietf.org/html/draft-ietf-dhc-failover-12http://tools.ietf.org/html/draft-ietf-dhc-failover-12


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( ne! "ailover 3elationship can be con$gured "or Hot-standby mode and even an e.isting relationshipin load balancing mode can be converted to hot-standby mode and vice-versa%

9peration in Hot Standby mode

:nli&e the ,oad 4alance mode !here the DHCP servers compute a hash o" the M(C address o" the

clients and decide !hether to respond to the client or not in hot standby mode the servers do notcompute hash o" the M(C address o" clients% +he active server responds to all client re#uests and thestandby server does not respond to any client re#uests at all !hile operating in ;93M(, state% 1henactive server goes do!n the standby server transitions into Communication Interrupted state andstarts responding to the clients% 9nce the active server is up the standby server retreats into standbymode and stops responding to clients% +his "acilitates "ailbac& o" the clients bac& to the active server%


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Step-by-Step: Confgure

DHCP or ai!o"er< out o" 6 rated this help"ul - 3ate this topic

Published2 February = 8

:pdated2 February = 8

(pplies +o2 1indo!s Server 8

Dynamic Host Con$guration Protocol 'DHCP) "ailover in 1indo!s Server 8 is a ne!

method "or ensuring continuous availability o" DHCP service to clients%

#n t$i% guide

+his guide provides step-by-step instructions "or deploying DHCP "ailover in a test lab using

t!o server computers and one client computer% So"t!are and hard!are re#uirements are

provided as !ell as an overvie! o" DHCP "ailover%

#&portant

+he "ollo!ing instructions are "or con$guring a test lab using the minimum number o" com

on the net!or& and to clearly sho! the desired "unctionality% +his con$guration is neither d

recommended con$guration "or a production net!or&% +he con$guration including IP addr

separate test lab net!or&%

DHCP ai!o"er o"er"ie'

In 1indo!s Server? @ 3 there are t!o high availability options available "or DHCPServer deployment% /ach o" these options is associated !ith some challenges%

8% DHCP in a (indo'% ai!o"er )!u%ter% +his option places the DHCP server in a

cluster !ith an additional server con$gured !ith the DHCP service that assumes the

load i" the primary DHCP server "ails% +he clustering deployment option uses a single

shared storage% +his ma&es the storage a single point o" "ailure and re#uires

additional investment in redundancy "or storage% In addition clustering involves

relatively comple. setup and maintenance%

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% Sp!it %)ope DHCP% Split scope DHCP uses t!o independent DHCP servers that share

responsibility "or a scope% +ypically A7 o" the addresses in the scope are assigned to

the primary server and the remaining


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server that has the role o" a primary "or a given subnet could be a secondary server "or

another subnet%

Hot standby mode o" operation is best suited to deployments !here a central oce or data

center server acts as a standby bac&up server to a server at a remote site !hich is local to

the DHCP clients 'e.2 hub and spo&e deployment)% In such deployments it is undesirable tohave a remote standby server service any clients unless the local DHCP server becomes

unavailable% +he $gure belo! is an e.ample o" a hub and spo&e deployment%

,oad sharing mode

In a load sharing mode deployment !hich is the de"ault mode o" operation the t!o servers

simultaneously serve IP addresses and options to clients on a given subnet% +he client

re#uests are load balanced and shared bet!een the t!o servers%

+he load sharing mode o" operation is best suited to deployments !here both servers in a

"ailover relationship are located at the same physical site% 4oth servers respond to DHCP

client re#uests based on the load distribution ratio con$gured by the administrator% See the

"ollo!ing e.amples%

,oad sharing in a single site !ith a single subnet

In the "ollo!ing e.ample t!o DHCP servers simultaneously provide IP addressing to clients

on a single subnet%

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,oad sharing in a single site !ith multiple subnets

In the "ollo!ing e.ample t!o DHCP servers simultaneously provide IP addressing to clients

on multiple subnets%

S)enario o"er"ie'

+his test lab demonstrates ne! DHCP "unctionality in 1indo!s Server 8% +!o server

computers and one client computer are used% See the "ollo!ing $gure%



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Hard!are and so"t!are re#uirements

+!o server computers and one client computer are re#uired to complete the test lab%

+he "ollo!ing are re#uired components o" the test lab2

8% +he product disc or other installation media "or 1indo!s Server 8%

% +!o computers that meet the minimum hard!are re#uirements "or 1indo!s Server

8%


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#&portant

Domain controller and D;S server roles are not re#uired "or DHCP "ailover% +hese ro

can also be con$gured on a !or&group computer 'not demonstrated in this test lab

% Con$gure DHCP2 DHCP is a DHCP server and domain member computer%


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+o install the operating system and con$gure +CP*IPon DHCP8

8% Start your computer using the 1indo!s Server 8 product disc or other digital

media%

% 1hen prompted enter a product &ey accept license terms con$gure cloc&

language and regional settings and provide a pass!ord "or the local (dministrator

account%


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DHCP8 !ill serve as a domain controller D;S server and DHCP server "or the contoso%com

(ctive Directory domain%

+o con$gure DHCP8 as a domain controller D;Sserver and DHCP server

8% +he Server Manager Dashboard is displayed by de"ault% In the navigation pane

clic& Confgure t$i% !o)a! %er"er%

% :nder PP/+#/S clic& the name ne.t to Co&puter na&e% +he Sy%te&

Propertie% dialog bo. !ill open%


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8A% In the A)ti"e Dire)tory Do&ain Ser"i)e% Confguration (i,ard onthe Dep!oy&ent Confguration page choose Add a ne' ore%t and then ne.t

to oot do&ain na&e type )onto%o.)o&%

8@%Clic& *e


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Practices'http2**go%microso"t%com*"!lin&*p*,in&IDGe)t ? %er dialog bo. type u%er1 under %er !ogon na&e and ne.t

to u!! na&e then clic& *e


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% 9n the Server Manager menu clic& the ;oti$cation >ag and then clic& Co&p!ete

DHCP )onfguration%

5% In the DHCP Po%t-#n%ta!! )onfguration 'i,ard clic& Co&&it and then

clic& C!o%e%

Confgure DHCP2

DHCP is a computer running 1indo!s Server? 8 providing the "ollo!ing services2

• ( DHCP server%

Initial con$guration o" DHCP consists o" the "ollo!ing steps2

• Install the operating system and con$gure +CP*IP on DHCP

• Install and con$gure DHCP on DHCP

During the demonstration portion o" the test lab DHCP !ill be used to create a "ailover

relationship !ith DHCP8%

Install the operating system and con$gure +CP*IP onDHCP

+ip

+he procedure belo! is identical to the steps used to install the operating system and con

an IP address o" 8%%%%

+o install the operating system and con$gure +CP*IPon DHCP

8% Start your computer using the 1indo!s Server 8 product disc or other digital

media%

% 1hen prompted enter a product &ey accept license terms con$gure cloc&

language and regional settings and provide a pass!ord "or the local (dministrator

account%

http://void%280%29/https://technet.microsoft.com/en-us/library/hh831385.aspx#dhcp2_1https://technet.microsoft.com/en-us/library/hh831385.aspx#dhcp2_2http://void%280%29/http://void%280%29/http://void%280%29/http://void%280%29/http://void%280%29/https://technet.microsoft.com/en-us/library/hh831385.aspx#dhcp2_1https://technet.microsoft.com/en-us/library/hh831385.aspx#dhcp2_2http://void%280%29/http://void%280%29/http://void%280%29/http://void%280%29/


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@% In Server Manager under Confgure t$i% !o)a! %er"er clic& Add o!e% and

eature%%

=% In the Add o!e% and eature% (i,ard clic& *e


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8% In the DHCP console tree right-clic& dhcp%contoso%com and then clic& (uthoriBe%

88% 3e"resh the vie! in the DHCP console and veri"y that DHCP is authoriBed and that

the Contoso-scope8 is active%

;ote2 +o revie! scopes on the current server using 1indo!s Po!erShell right-clic& (indo'% Po'erS$e!! clic& un a% Ad&ini%trator clic& e% in the :ser

(ccount Control alert that appears and then type the "ollo!ing command at the

1indo!s Po!erShell prompt and then press /;+/3%

get-dhcpserverv4scope

PS C:\Windows\system32> get-dhcpserverv4scope

ScopeId Subnet!s" #!me St!te St!rt$!nge

%nd$!nge &e!se'ur!tion

------- ---------- ---- ----- ----------

-------- -------------

()*)*)*) 2++*2++*2++*) Contoso-scope( ,ctive ()*)*)*(

()*)*)*2+4 )):)2:))

Confgure C!ient1

Client8 is a computer running 1indo!s? @ that is acting as a DHCP client%

Con$guration o" Client8 consists o" the "ollo!ing steps2

• Install the operating system on Client8

• Pin 1indo!s Po!erShell to the tas&bar

During the demonstration portion o" the test lab Client8 !ill be used as a DHCP client%

Install the operating system on Client8

+o install the operating system on Client8

8% Start your computer using the 1indo!s @ product disc or other digital media%

% 1hen prompted enter a product &ey and accept license terms%


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6% ;e.t to %er na&e type u%er1 enter a pass!ord and pass!ord hint and then

clic& ini%$%

Pin 1indo!s Po!erShell to the tas&bar

+he DHCP "ailover demonstration on Client8 ma&es use o" 1indo!s Po!erShell to veri"yDHCP lease in"ormation% +o ma&e 1indo!s Po!erShell more easily accessible it !ill be

pinned to the tas&bar%

+o pin 1indo!s Po!erShell to the tas&bar

8% +he Start menu is displayed by de"ault% I" Start is not displayed move the mouse

cursor to the lo!er le"t corner o" the screen until Start is displayed and then

clic& Start%

% +ype po'er and then under e%u!t% or po'erE right-clic& (indo'%

Po'erS$e!! and then clic& Pin to ta%bar%Con$rm that 1indo!s Po!erShell is

pinned to the tas&bar%

*ote

Client8 can also be oined to the contoso%com domain ho!ever this is not re#uired to com

DHCP ai!o"er de&on%tration

For the DHCP "ailover demonstration portion o" the test lab a "ailover relationship !ill be

created using DHCP8 and DHCP%

( demonstration o" DHCP "ailover on 1indo!s Server 8 consists o" the "ollo!ing

procedures2

8% Con$gure a "ailover relationship

% Jie! or edit properties o" the "ailover con$guration


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First con$gure a "ailover relationship using DHCP8 and DHCP%

+o con$gure a "ailover relationship

8% 9n DHCP open the DHCP console right-clic& the Conto%o-%)ope1 DHCP scope and

then clic& Confgure ai!o"er%

% In the Confgure ai!o"er !iBard clic& *e


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+he Ma.imum Client ,ead +ime 'MC,+) is additional time provided to a DHCP client

primary to the secondary server in the C9;;/C+ message and is the ma.imum am

time &no!n by the partner server%

+he 8 minute MC,+ value used here is "or test lab purposes only to prompt lease re

longer MC,+ such as 8 hour%

A% 3evie! the options available in the drop-do!n menu ne.t to Mode% 0ou can

choose oad ba!an)e or Hot %tandby% 4y de"ault oad ba!an)e mode is chosen%

@% Clic& *e


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8% 9n DHCP8 re"resh the DHCP console and veri"y that the same DHCP scope

con$guration that is present on DHCP is no! present on DHCP8%

Jie! or edit properties o" the "ailover con$guration

("ter you con$gure a "ailover relationship on a DHCP server details "or the "ailover

relationship are displayed in the DHCP console%

+o vie! or edit properties o" the "ailover relationship8% 9n DHCP8 or DHCP in the DHCP console right-clic& the Conto%o-%)ope1 DHCP

scope and then clic& Propertie%%

% Clic& the ai!o"er tab and revie! the in"ormation displayed% Jeri"y that *or&a! is

displayed ne.t to State o t$i% Ser"er and also ne.t to State o Partner Ser"er%



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% Clic& /dit and revie! properties o" the "ailover relationship that are available to edit%

5% ,eave the dialog bo. open "or the "ollo!ing procedure%

/dit properties o" the "ailover relationship anddemonstrate load balancing

+o demonstrate dynamic load balancing properties o" the "ailover relationship the load

balancing percentage !ill be changed "or an active DHCP scope%

+o edit properties o" the "ailover relationship anddemonstrate load balancing

8% 9n Client8 clic& (indo'% Po'erS$e!! and type the "ollo!ing command%

2* ipconig .!//


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% In the ie'6/dit ai!o"er e!ation%$ip dialog bo. DHCP8 or DHCP that !as

opened in the previous procedure change the values under oad Fa!an)e

Mode ne.t to o)a! Ser"er and Partner Ser"er so that 100G is assigned to the

DHCP server that is currently not supplying an IP address to Client8% +he server that

is currently supplying an IP address to Client8 !ill have a value assigned o" 0G%

5% Clic& ; t!ice !ait until the current DHCP lease is e.pired on Client8 and then

type ip)onfg 6a!! again at the 1indo!s Po!erShell prompt%

6% ;ote that the DHCP server that is supplying an IP address con$guration to Client8 has

changed to the server that you assigned 87 !eight in load balancing mode%

/dit properties o" the "ailover relationship anddemonstrate hot standby mode

+o demonstrate hot standby mode the DHCP Server service on one o" the "ailover partners

!ill be stopped%

+o edit properties o" the "ailover relationship anddemonstrate hot standby mode

8% 9n DHCP8 or DHCP in the DHCP console right-clic& the Conto%o-%)ope1 DHCP

scope and then clic& Propertie%%

% Clic& the ai!o"er tab%


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+ip

+he server that is designated to be (ctive in hot standby mode is the server that yo

5% Clic& ; t!ice and then !ait minutes "or the DHCP lease on Client8 to rene!%

6% 9n Client8 type ip)onfg 6a!! at the 1indo!s Po!erShell prompt and veri"y that the

server that is assigned as (ctive is supplying an IP addresses con$guration to Client8%

A% In the DHCP console on the DHCP server that is mar&ed as A)ti"e "or the hot standby

"ailover relationship and is currently supplying an IP address to Client8 right-clic& the

server name point to (ll +as&s and then clic& Stop%

@% Jeri"y that the DHCP service is stopped on the active DHCP server%

=% 1ait "or the DHCP lease to rene! on Client8 type ip)onfg 6a!! at the 1indo!s

Po!erShell prompt and veri"y that the standby DHCP server is supplying an IP

address to Client8%


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Con)!u%ion

DHCP "ailover provides high availability o" DHCP services !ithout the challenges o"

clustering or split scope DHCP% 4ene$ts o" DHCP "ailover include2

8% Si&p!e2 ( !iBard is provided to create DHCP "ailover relationships bet!een DHCPservers% +he !iBard automatically replicates scopes and settings "rom the primary

server to the "ailover partner%

% !e


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Ma. client lead time vs ,ease time

In a de"ault con$guration o" a DHCP "ailover pair clients seem to sometimes get leases as long as

the scopeKs de"ault lease time '@ days) and sometimes get leases as long as the scopeKs de"ault ma.

client lead time '8 hour)% It also seems depending on the KmoodK o" the client that the short leases do

not al!ays rene! into long ones% (dusting the MC,+ results in the short leasesK length changing to!hatever the MC,+ is% +his seems to happen !hether using load balancing or hot standby%

1hy !ould clients get such a short lease time !hen itKs de$ned to be much longer in the scope Is it

because the client got a response "rom the standby server be"ore the primary server and it uses the

MC,+ as a transition "rom the standby server to the primary server It might not be because the delay

setting "or each mirror o" a scope can be set separately "or instance ms on the primaryKs scopes and

8ms on the secondaryKs scopesL triggering replication does not replicate this setting%

ordon Fecy&

8*8*8<

3e #uestions

8% this is supported "or any DHCP client - the client is not actually a!are o" the "ail over mechanism - it

ust !or&s%

% +his mechanism only !or&s in Server 8 and 8 3 - the only KpatchK is th
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