The document discusses Takuya Asada's work implementing BCube, a new network architecture designed for modular data centers, for Linux. Some key points: 1) BCube uses servers as both end hosts and relay nodes, allowing for high network capacity and graceful performance degradation as servers/switches fail. 2) Asada leveraged existing Linux bridge code as a starting point, modifying it to support BCube addressing and routing. 3) Current implementation supports basic routing but not more advanced features like source routing or failure handling; evaluation on a testbed is planned.

1. Takuya ASADA<syuu@dokukino.com>
@syuu1228

2.  I was in embedded software company,
worked on SMP support for router firmware
 Ph. D. Student of Tokyo University of Technology,
researching improvement network I/O
architecture on modern x86 servers
 Interested in: SMP, Network, Virtualization
 GSoC ’11(FreeBSD) Multithread support for BPF
 GSoC ’12(FreeBSD) BIOS support for BHyVe
 Research assistant at IIJ research laboratory,
implementing BCube for Linux
Today’s topic!

3.  BCube is a new network architecture
 Designed for shipping-container based
modular data centers
 Server-centric network structure
◦ Server act as
 End hosts
 Relay nodes for each other
 The paper published in ACM SIGCOMM ’09 by
Microsoft Research Asia

4.  Each server has one connection to each layers
 Switches never connect to other switches
 Servers relay traffic for each other
2,0 2,1 2,0 2,1
1,0 1,1 1,0 1,1
0,0 0,1 0,0 0,1
000 001 010 011 100 101 110 111
switch
Bcube0
Bcube1 server
Bcube2

5.  𝐵𝐶𝑢𝑏𝑒 𝑘 has k + 1 layers
 𝐵𝐶𝑢𝑏𝑒 𝑥 contains n 𝐵𝐶𝑢𝑏𝑒 𝑥−1
 𝐵𝐶𝑢𝑏𝑒0 contains n servers
 Total servers = 𝑛 𝑘+1
2,0 2,1 2,0 2,1
1,0 1,1 1,0 1,1
0,0 0,1 0,0 0,1
000 001 010 011 100 101 110 111
switch
Bcube0
Bcube1 server
Bcube2

6.  High network capacity for various traffic
patterns
◦ one-to-one
◦ one-to-all
◦ one-to-several
◦ all-to-all
 Performance degrades gracefully as
servers/switches failure increases
 Doesn’t need special hardware, only use
commodity switch

7.  Each server has unique BCube address
 Each digit pointed port number of switch in
the layer
2,0 2,1 2,0 2,1
1,0 1,1 1,0 1,1
0,0 0,1 0,0 0,1
000 001 010 011 100 101 110 111
Bcube0
switch
Bcube1 server
Bcube2

8.  Default routing rule
◦ Top layer→Bottom layer
◦ Ex: Route from 000 to 111
000 →100 →110 →111
2,0 2,1 2,0 2,1
1,0 1,1 1,0 1,1
0,0 0,1 0,0 0,1
000 001 010 011 100 101 110 111
Bcube0
Bcube1
Bcube2

9.  There are alternate routes between any nodes
 Can bypass failure servers and switches
 Also can use acceralate throughput to
parallelize traffic
2,0 2,1 2,0 2,1
1,0 1,1 1,0 1,1
0,0 0,1 0,0 0,1
000 001 010 011 100 101 110 111
Bcube0
Bcube1
Bcube2

10.  Source server decides the best path for a flow
 Bypass failure paths
 To propagate routing path, source server
writes routing path information on packet
header

11.  Add BCube header between Ethernet header
and IP header
 Has src/dst address and also routing path
information on “Next Hop Index Array”
Ethernet Header
BCube dest address
BCube source address
BCube Header
Protocol type
IP Header Next Hop Index Array

12.  Evaluating various "Data Center Network"
technologies, especially for container-
moduler datacenter architecture.
BCube is one of the candidate.

13.  Try to use existing code as much as possible
 Minimum implementation at first
 BCube binds multiple interface,
assigns a BCube address and an IP address
 What is the most similar function which
already existing on Linux? →Bridge!
◦ Forked bridge.ko and brctl command,
named bcube.ko and bcctl command

14.  brctl addbr <bridge>
brctl delbr <bridge>
↓
bcctl addbc <bcube> <bcaddr> <N> <K>
bcctl delbc <bcube>
 Modified addbr/delbr, add 3 args
◦ BCube address
◦ n and k parameter
 Use MAC address format/size for BCube address
101 → 00:00:01:00:01
 Use BCube address for HW address of BCube
device
◦ It works like fake MAC address on Linux network stack

15.  brctl addif <bridge> <device>
brctl delif <bridge> <device>
↓
bcctl assignif <bcube> <layer> <device>
bcctl unassignif <bcube> <layer> <device>
 Modified assignif / unassignif command, add
layer number on args

16.  Need to reconsider address resolution
 Normal Ethernet
◦ IP Address → MAC Address (ARP)
 BCube network
◦ IP Address → BCube Address
→ ARP?
◦ (Neighbor) BCube address → MAC Address
→ Need additional neighbor discovery protocol

17.  Once broadcast works on BCube
implementation, ARP should work on it
 But I haven’t implemented it yet, decided to
configure manually by following command:
arp –i bc0 –s 10.0.0.6 00:00:00:01:00:10

18.  Need an ARP like protocol
 Decided to configure manually too,
implemented following command:
bcctl addneighbour <bcube> <layer>
<bcaddr> <macaddr>
bcctl delneighbour <bcube> <layer>
<bcaddr>
 bcube.ko maintenance neighbor table, use it
in packet transmitting/forwarding

19.  In bridge.ko, it maintenance FDB(forwarding
database) to lookup destination MAC
address→output port using hash table
 Deleted FDB, implemented function to decide
next hop BCube address, output port, and
MAC address of next hop
 Haven’t implemented source routing – just
default routing for now

20.  Top layer→Bottom layer
 Ex: Route from 000 to 111
000 →100 →110 →111
2,0 2,1 2,0 2,1
1,0 1,1 1,0 1,1
0,0 0,1 0,0 0,1
000 001 010 011 100 101 110 111
Bcube0
Bcube1
Bcube2

21.  To add BCube Header between Ethernet Header
and IP header, I forked net/ethernet/eth.c
 ETH_HLEN (14byte)
→ BCUBE_HLEN (24byte)
 struct ethhdr (MAC header)
→ struct bcubehdr (MAC & BCube header)
 eth_header_ops → bc_header_ops
To handle Bcube Header
 Unfortunately GRO accesses ethernet header
directly, and it works before BCube handles a
packet – need to disable it

22.  Found a way to implement new L2 framework
using existing bridge implementation
◦ Lot more easy than implement it from scrach
 Development Status
◦ Implemented basic features, debugging now
◦ Will consider to add more features
 broadcast / multicast
 Intermediate node/switch failure detection, change the
routing
 source routing
 address resolution protocol
 Planing more detail evaluation in our data center
testbed
 Any comments and suggestions are welcome 

23. This work was done as part of research
assistance work at IIJ research laboratory.