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SmartARP:
Making Gigabit Networks Cheap
Andris Sidorovs, Riga Technical University
Janis Lacis, Latnet
Karlis Ogsts, Tieto Konts Financial Systems Ltd.
Guntis Barzdins, Taide Network AS
Janis Dzerins, University of Latvia
Ethernet
IP: 10.0.0.10
IP: 10.0.0.11
MAC: 00:00:aa:aa:aa:aa
MAC: 00:00:bb:bb:bb:bb
A
B
C
D
IP: 10.0.0.12
IP: 10.0.0.13
MAC: 00:00:cc:cc:cc:cc
MAC: 00:00:dd:dd:dd:dd
• Most popular LAN technology
nowadays 10Mb/s - 1Gb/s
• Each host has unique 48bit
MAC address (factory assigned)
• Frames sent to MAC addresses
• Broadcasts widely used
• To find destination MAC
address, ARP protocol is used
Ethernet frame
Dest
MAC
Source
MAC
Dest
IP
Source
IP
IP packet
Data
ARP: finding the MAC Address
Host A
ARP Query
Broadcast
Host B
MAC ?
Host B
Host B
IP
ARP Response
Host B
Unicast
MAC
Host B
IP
RFC 826: Address Resolution Protocol, 1982
Interconnecting Ethernet LANs
?
?
?
?
Departmental LANs in
University Campus
Requirements
• Interconnections must be fast
• Departmental Novell and MS
Windows networks should be
isolated
• Misconfiguration in one
department should not disrupt
network in another department
• Easy to configure
Interconnecting by Routers
Departmental LANs in
University Campus
Advantages
• Contain broadcasts
• Filtering possible by protocol
Disadvantages
• Slow (each packet intensively
processed)
• Complex
• Expensive (especially for
100Mbps and 1Gbps)
Interconnecting by LAN Switches
Advantages
• Fast (wire speed)
• Cheap
• Simple to install
Disadvantages
• Do not scale, because
broadcasts are not contained
• No filtering by protocol
Departmental LANs in
University Campus
Interconnecting by VLANs
VLAN 1
VLAN 4
Advantages
Bottleneck
• Single powerful router
VLAN 2
interconnects many VLANs
• Cisco Netflow and Routing
Switches shortcut traffic
Disadvantages
• Bottleneck is router
• Only expensive switches and
routers support that
VLAN 3
Interconnecting by SmartARP
MAC
Broadcast filter
Advantages
• Contains Broadcasts
• Effectively stops all protocols
• Fast (wire speed)
• Cheap (standard switches used)
Disadvantages
• Nothing works ...
... unless smartARP used
SmartARP
•
•
•
•
•
•
•
Server based ARP
Transparent to hosts
Uses queries instead of broadcasts
Easy to configure (stateless)
Only one needed per broadcast domain
Available for free (runs on Win95 & Linux)
Supports 10Mb/s, 100Mb/s, 1Gb/s, ...
SmartARP operation
MAC
Broadcast filter
X
A
B
1
SmartARP
Server
SmartARP
Server
ARP Reply
4
Broadcast
Y
2
Unicast
3
SmartARP
Server
ARP Query
D
C
SmartARP
Server
SmartARP configuration
Workgroups are
assigned smaller
continuous
ranges of IP
addresses
A
SmartARP
Server A
10.1.1.0 10.1.1.255
10.1.4.0 10.1.4.255
D
SmartARP
Server D
MAC
Broadcast
filter
SmartARP
Server B
B
10.1.2.0 10.1.2.255
10.1.3.0 10.1.3.255
SmartARP
Server C
Whole network is one big IP subnet 10.1.0.0/16
C
SmartARP config file
Configuration file of SmartARP server A:
10.1.1.0
10.1.2.0
10.1.3.0
10.1.4.0
255.255.255.0
255.255.255.0
255.255.255.0
255.255.255.0
local
forward 00:01:3a:4c:12
forward 00:73:18:a5:62
forward 00:0c:63:52:7a
Ranges of IP addresses
assigned to workgroups
MAC address
of smartARP
server B
MAC address
of smartARP
server C
MAC address
of smartARP
server D
SmartARP implementation Win95
SmartARP implementation Linux
•
•
•
•
Source code available
Runs on multiple interfaces
Can be used with Linux bridge
Convenient pre-compiled version:
– boots from single 1.44MB FDD (no HDD needed)
– optionally acts as bridge with MAC broadcast filter
– supports up to six NE2000 PCI compatible
10/100Mbps Ethernet cards
– “Cisco IOS like” interface for easy use
Advanced SmartARP features
IP Address and Mask
Action
10.1.1.0
10.1.2.0
10.1.7.2
10.1.3.0
10.1.3.1
10.2.2.0
10.3.3.0
LOCAL
FORWARD 00:00:00:11:11:11
CONST 00:00:22:d5:e6:f7
IP
00:11
SILENT
DNS
mac.mydomain.com
PROXY 10.1.1.2
255.255.255.0
255.255.255.0
255.255.255.255
255.255.255.0
255.255.255.255
255.255.255.0
255.255.255.0
Parameter
Like in routing, IP network number with longest prefix is
preferred when selecting a SmartARP rule to be applied
How to filter broadcasts in switches?
• None of configurable Cisco, Bay, 3Com
switches has such option (!!!)
• Use Linux bridge code - modify one line in
source code to filter Broadcasts
• Use any Cisco router as Ethernet bridge:
no ip routing
bridge 1 protocol ieee
bridge 1 address ffff.ffff.ffff discard
interface Ethernet0
no ip address
bridge-group 1
interface Ethernet1
no ip address
bridge-group 1
Cheap Scaleable Ethernet: HANE
Hierarchically Addressed Non-broadcast Ethernet
– Ethernet without MAC broadcasts
– 48bit MAC addresses are not factory assigned,
but are configurable like IP addresses
(32bit IP address can be part of 48bit MAC address)
– Ethernet switches use prefix based MAC switching
tables
HANE is the way to go: it is cheap, fast, scales to global
networks, and is compatible with existing networks.
How to change MAC address?
24 bits
24 bits
Vendor Code
Serial Number
0000.3c12. 3456
ROM
RAM
Interface driver copies MAC
address from ROM into RAM
by default, if no explicit MAC
address is supplied to the driver
• Factory assigned unique MAC address is burned into ROM, but the
MAC address actually used by the card is stored in RAM
• MAC address is configurable in Win95, NT, UNIX, Cisco routers
(instructions provided in Full Paper)
Final
• More details appear in Full Paper (TNNC’99
Conference Proceedings)
• SmartARP software available at:
http://www.ltn.lv/~guntis/smarp/
• Contact authors for latest smartARP versions:
[email protected], [email protected], [email protected],
[email protected], [email protected]