def getL3BridgeConfig(update):
    """
    Creates configuration sections for layer 3 bridging.
    """
    interfaces = update.cache_get('networkInterfaces')
    parprouted = list()
    for iface in interfaces:
        l3bridge = iface.get('l3bridge', None)
        if l3bridge is None:
            continue
        config = {'type': 'bridge'}
        options = {'interfaces': [iface['externalIntf'], l3bridge]}
        parprouted.append((config, options))
    update.cache_set('parproutedConfig', parprouted)
