1. Introduction to Smart-Relay

  • Relay Agent 장비는 처음 Discover 메시지를 서버로 전송할 때 "Gateway IP Address"에 Primary IP Address를 넣어 전송
  • Smart-Relay는 Offer 메시지를 수신하지 못하면 Primary IP Address를 사용하여 3번의 Discover 메시지를 서버로 전송
  • 그래도 Offer 메시지를 수신하지 못하면 Relay Agent(Smart-Relay)는 "Gateway IP Address"에 Secondary IP Address를 넣어 전송
  • 그래도 Offer 메시지를 수신하지 못하면 Relay Agent(Smart-Relay)는 "Gateway IP Address"에 다음 IP Address를 넣어 전송
  • Relay Agent(Smart-Relay)는 Secondary IP Address로 모두 시도되었지만 아직도 Offer 메시지를 수신하지 못하면 Primary IP Address부터 시작하여 프로세스를 반복
  • Smart-Relay 기능이 없으면 Relay Agent는 모든 Discover 메시지의 "Gateway IP Address"에 Primary IP Address만 넣어 전송

 

 

2. DHCP Smart-Relay Configuration 구성도

1) DHCP Smart-Relay Configuration 구성도

  • DHCP 기본 개념, DHCP 동작 과정, DHCP Relay Agent 동작 과정, DHCP Basic Configuration, DHCP Relay Agent Configuration을 먼저 학습하는 것을 권고

 

2) 테스트 장비

  • Emulator : EVE-NG 
  • OS : Cisco IOL I86BI_LINUXL2-ADVENTERPRISEK9-M, Version 15.1c

 

 

3. DHCP Smart-Relay Configuration

1) Relay Agent Interface IP Address Configuration

더보기 
< Loopback Interface IP Address 구성 >
RELAY-AGENT(config)#interface lo0
RELAY-AGENT(config-if)#ip address 1.1.1.1 255.255.255.0
RELAY-AGENT(config-if)#no shutdown 

< e0/2 Interface IP Address 구성 >
RELAY-AGENT(config)#interface e0/2
RELAY-AGENT(config-if)#no switchport 
RELAY-AGENT(config-if)#ip address 1.1.2.1 255.255.255.0

< VLAN 생성 >
RELAY-AGENT(config)#vlan 10
RELAY-AGENT(config-vlan)#name VLAN10

< Interface에 VLAN Bidning >
RELAY-AGENT(config)#interface e0/0
RELAY-AGENT(config-if)#switchport mode access
RELAY-AGENT(config-if)#switchport access vlan 10
RELAY-AGENT(config-if)#no cdp enable

RELAY-AGENT(config)#interface e0/1
RELAY-AGENT(config-if)#switchport mode access
RELAY-AGENT(config-if)#switchport access vlan 10
RELAY-AGENT(config-if)#no cdp enable

< VLAN Interface에 IP Address 구성 >
RELAY-AGENT(config)#interface vlan 10
RELAY-AGENT(config-if)#ip address 10.0.0.1 255.255.255.0
RELAY-AGENT(config-if)#ip address 20.0.0.1 255.255.255.0 secondary
RELAY-AGENT(config-if)#no shutdown
  • Priamry IP Address와 Secondary IP Address를 설정

 

2) DHCP Server Interface IP Address Configuration

더보기 
< Loopback Interface IP Address 구성 >
DHCP-SERVER(config)#interface lo0
DHCP-SERVER(config-if)#ip address 2.2.2.2 255.255.255.0
DHCP-SERVER(config-if)#no shutdown 

< e0/0 Interface IP Address 구성 >
DHCP-SERVER(config)#interface e0/0
DHCP-SERVER(config-if)#no switchport 
DHCP-SERVER(config-if)#ip address 1.1.2.2 255.255.255.0
DHCP-SERVER(config-if)#no shutdown

 

3) DHCP Server Routing Configuration

DHCP-SERVER(config)#ip route 10.0.0.0 255.255.255.0 1.1.2.1
DHCP-SERVER(config)#ip route 20.0.0.0 255.255.255.0 1.1.2.1
  • Relay Agent 장비에서 DHCP 메시지를 Broadcast→Unicast로 변경하여 서버로 전송하면 서버는 Relay Agent의 Downlink IP Address로 DHCP 메시지를 전송해야 하므로 라우팅 정보가 필요

 

4)  DHCP Relay Agent Configuration

RELAY-AGENT(config)#interface vlan 10
RELAY-AGENT(config-if)#ip helper-address 1.1.2.2	## 해당 인터페이스로 DHCP 메시지 수신 시, 설정한 IP Address(DHCP Server)로 전송

 

5) DHCP Pool Configuration

< DHCP Pool 구성 >
DHCP-SERVER(config)#ip dhcp pool POOL-10 
DHCP-SERVER(dhcp-config)#network 10.0.0.0 255.255.255.0   
DHCP-SERVER(dhcp-config)#default-router 10.0.0.1
DHCP-SERVER(dhcp-config)#lease 0 0 5

DHCP-SERVER(config)#ip dhcp pool POOL-20
DHCP-SERVER(dhcp-config)#network 20.0.0.0 255.255.255.0
DHCP-SERVER(dhcp-config)#default-router 20.0.0.1 
DHCP-SERVER(dhcp-config)#lease 0 0 5

< DHCP Pool에서제외할 IP Range 구성 >
DHCP-SERVER(config)#ip dhcp excluded-address 10.0.0.1 10.0.0.253
DHCP-SERVER(config)#ip dhcp excluded-address 20.0.0.1 20.0.0.253
  • 테스트를 위해 각 Pool에서 하나의 IP Address만 할당되도록 "excluded-address"를 구성

 

6) CLIENT-1 DHCP Enable

CLIENT-1(config)#interface e0/0
CLIENT-1(config-if)#no switchport
CLIENT-1(config-if)#ip address dhcp
CLIENT-1(config-if)#no shutdown

CLIENT-1#show ip interface brief e0/0
Interface              IP-Address      OK? Method Status                Protocol
Ethernet0/0            10.0.0.254      YES DHCP   up                    up
  • CLIENT-1 장비는 DHCP를 사용하여 10.0.0.254 IP Address를 할당

 

7) Smart-Relay Enable before CLIENT-2 DHCP Enable

CLIENT-2(config)#interface e0/0
CLIENT-2(config-if)#no switchport
CLIENT-2(config-if)#ip address dhcp
CLIENT-2(config-if)#no shutdown

  • Relay Agent에서 "Gateway IP Address"필드에 Primary IP Address만 채워 전송하므로 DHCP 서버는 10.0.0.1이 해당하는 Pool만 고려하여 IP Address 할당 시도

 

8) Smart-Relay Configuration

RELAY-AGENT(config)#ip dhcp smart-relay
  • Smart-Relay 기능 활성화

 

9) Smart-Relay Enable after CLIENT-2 DHCP Enable

CLIENT-2(config)#interface e0/0
CLIENT-2(config-if)#no shutdown

  • Relay Agent는 "Gateway IP Address"필드에 Primary IP Address를 넣어 전송하고 3번 실패하면 "Gateway IP Address"필드에 Secondary IP Address를 넣어 전송하여 DHCP 서버는 20.0.0.1이 해당하는 Pool을 고려하여 IP Address를 할당
  • Relay Agent는 Source-IP를 Primary IP Address로 구성하며 DHCP 서버는 Destination-IP는 IP Address를 할당할 네트워크에 해당하는 Secondary IP Address로 구성

 

10) DHCP CLIENT-1 확인

CLIENT-1#show ip route | begin Gateway
Gateway of last resort is 10.0.0.1 to network 0.0.0.0

S*    0.0.0.0/0 [254/0] via 10.0.0.1
      10.0.0.0/8 is variably subnetted, 2 subnets, 2 masks
C        10.0.0.0/24 is directly connected, Ethernet0/0
L        10.0.0.254/32 is directly connected, Ethernet0/0
CLIENT-1#show dhcp server 
   DHCP server: ANY (255.255.255.255)
    Leases:   4
    Offers:   1      Requests: 4     Acks : 4     Naks: 0
    Declines: 0      Releases: 0     Query: 0     Bad: 0
    Subnet: 255.255.255.0
CLIENT-1#show dhcp lease 
Temp IP addr: 10.0.0.254  for peer on Interface: Ethernet0/0
Temp  sub net mask: 255.255.255.0
   DHCP Lease server: 1.1.2.2, state: 5 Bound
   DHCP transaction id: 2126
   Lease: 300 secs,  Renewal: 150 secs,  Rebind: 259 secs
Temp default-gateway addr: 10.0.0.1
   Next timer fires after: 00:02:08
   Retry count: 0   Client-ID: cisco-aabb.cc03.7000-Et0/0
   Client-ID hex dump: 636973636F2D616162622E636330332E
                       373030302D4574302F30
   Hostname: CLIENT-1

 

11) DHCP CLIENT-2 확인

CLIENT-2#show ip route | begin Gateway
Gateway of last resort is 20.0.0.1 to network 0.0.0.0

S*    0.0.0.0/0 [254/0] via 20.0.0.1
      20.0.0.0/8 is variably subnetted, 2 subnets, 2 masks
C        20.0.0.0/24 is directly connected, Ethernet0/0
L        20.0.0.254/32 is directly connected, Ethernet0/0
CLIENT-2#show dhcp server
   DHCP server: ANY (255.255.255.255)
    Leases:   3
    Offers:   2      Requests: 3     Acks : 3     Naks: 0
    Declines: 0      Releases: 3     Query: 0     Bad: 0
    Subnet: 255.255.255.0
CLIENT-2#show dhcp lease 
Temp IP addr: 20.0.0.254  for peer on Interface: Ethernet0/0
Temp  sub net mask: 255.255.255.0
   DHCP Lease server: 1.1.2.2, state: 5 Bound
   DHCP transaction id: 205F
   Lease: 300 secs,  Renewal: 150 secs,  Rebind: 259 secs
Temp default-gateway addr: 20.0.0.1
   Next timer fires after: 00:00:13
   Retry count: 0   Client-ID: cisco-aabb.cc03.d000-Et0/0
   Client-ID hex dump: 636973636F2D616162622E636330332E
                       643030302D4574302F30
   Hostname: CLIENT-2

 

12) DHCP Server 확인

DHCP-SERVER#show ip dhcp pool 

Pool POOL-10 :
 Utilization mark (high/low)    : 100 / 0
 Subnet size (first/next)       : 0 / 0 
 Total addresses                : 254
 Leased addresses               : 1
 Excluded addresses             : 253
 Pending event                  : none
 1 subnet is currently in the pool :
 Current index        IP address range                    Leased/Excluded/Total
 0.0.0.0              10.0.0.1         - 10.0.0.254        1     / 253   / 254  

Pool POOL-20 :
 Utilization mark (high/low)    : 100 / 0
 Subnet size (first/next)       : 0 / 0 
 Total addresses                : 254
 Leased addresses               : 1
 Excluded addresses             : 253
 Pending event                  : none
 1 subnet is currently in the pool :
 Current index        IP address range                    Leased/Excluded/Total
 20.0.0.1             20.0.0.1         - 20.0.0.254        1     / 253   / 254
DHCP-SERVER#show ip dhcp binding 
Bindings from all pools not associated with VRF:
IP address          Client-ID/              Lease expiration        Type
                    Hardware address/
                    User name
10.0.0.254          0063.6973.636f.2d61.    Nov 24 2024 02:08 PM    Automatic
                    6162.622e.6363.3033.
                    2e37.3030.302d.4574.
                    302f.30
20.0.0.254          0063.6973.636f.2d61.    Nov 24 2024 02:09 PM    Automatic
                    6162.622e.6363.3033.
                    2e64.3030.302d.4574.
                    302f.30

 

13) Smart-Relay Renewal Message

  • Source IP는 이미 할당받은 IP Address로 구성
  • Unicast로 전송하므로 Relay Agent에서 재처리 과정 없이 DHCP 서버로 전송

 

14) Smart-Relay Release Message

CLIENT-2(config)#interface e0/0
CLIENT-2(config-if)#shutdown

  • Source IP는 이미 할당받은 IP Address로 구성
  • Unicast로 전송하므로 Relay Agent에서 재처리 과정 없이 DHCP 서버로 전송

 

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